Merci pour ta réponse, voici les logs du plantage original quand il y a eu rupture de réseau :
2021-06-23 06:53:28,676: DEBUG - Executing command '/bin/bash -x "./upgrade" 7>&1'
2021-06-23 06:53:28,701: DEBUG - + source _common.sh
2021-06-23 06:53:28,703: DEBUG - ++ pkg_dependencies='imagemagick libmagickcore-6.q16-6-extra acl tar smbclient at'
2021-06-23 06:53:28,704: DEBUG - ++ YNH_PHP_VERSION=7.3
2021-06-23 06:53:28,706: DEBUG - ++ extra_php_dependencies='php7.3-bz2 php7.3-imap php7.3-smbclient php7.3-gmp php7.3-gd php7.3-json php7.3-intl php7.3-curl php7.3-apcu php7.3-redis php7.3-ldap php7.3-imagick php7.3-zip php7.3-mbstring php7.3-xml php7.3-mysql php7.3-igbinary php7.3-bcmath'
2021-06-23 06:53:28,710: DEBUG - + source /usr/share/yunohost/helpers
2021-06-23 06:53:28,714: DEBUG - +++ set +o
2021-06-23 06:53:28,715: DEBUG - +++ grep xtrace
2021-06-23 06:53:28,721: DEBUG - ++ readonly 'XTRACE_ENABLE=set -o xtrace'
2021-06-23 06:53:28,722: DEBUG - ++ XTRACE_ENABLE='set -o xtrace'
2021-06-23 06:53:29,124: INFO - [....................] > Loading installation settings...
2021-06-23 06:53:29,126: DEBUG - + echo '[....................] > Loading installation settings...'
2021-06-23 06:53:29,129: DEBUG - + app=nextcloud
2021-06-23 06:53:29,129: DEBUG - ++ ynh_app_setting_get --app=nextcloud --key=domain
2021-06-23 06:53:29,252: DEBUG - ++ [[ domain =~ (unprotected|protected|skipped)_ ]]
2021-06-23 06:53:29,270: DEBUG - ++ ynh_app_setting get nextcloud domain
2021-06-23 06:53:29,559: DEBUG - + domain=nsi.ynh.fr
2021-06-23 06:53:29,561: DEBUG - ++ ynh_app_setting_get --app=nextcloud --key=path
2021-06-23 06:53:29,654: DEBUG - ++ [[ path =~ (unprotected|protected|skipped)_ ]]
2021-06-23 06:53:29,655: DEBUG - ++ ynh_app_setting get nextcloud path
2021-06-23 06:53:29,909: DEBUG - + path_url=/nextcloud
2021-06-23 06:53:29,911: DEBUG - ++ ynh_app_setting_get --app=nextcloud --key=admin
2021-06-23 06:53:30,004: DEBUG - ++ [[ admin =~ (unprotected|protected|skipped)_ ]]
2021-06-23 06:53:30,005: DEBUG - ++ ynh_app_setting get nextcloud admin
2021-06-23 06:53:30,266: DEBUG - + admin=yvesmarie
2021-06-23 06:53:30,268: DEBUG - ++ ynh_app_setting_get --app=nextcloud --key=final_path
2021-06-23 06:53:30,386: DEBUG - ++ [[ final_path =~ (unprotected|protected|skipped)_ ]]
2021-06-23 06:53:30,387: DEBUG - ++ ynh_app_setting get nextcloud final_path
2021-06-23 06:53:30,649: DEBUG - + final_path=/var/www/nextcloud
2021-06-23 06:53:30,651: DEBUG - ++ ynh_app_setting_get --app=nextcloud --key=db_name
2021-06-23 06:53:30,744: DEBUG - ++ [[ db_name =~ (unprotected|protected|skipped)_ ]]
2021-06-23 06:53:30,746: DEBUG - ++ ynh_app_setting get nextcloud db_name
2021-06-23 06:53:31,000: DEBUG - + db_name=nextcloud
2021-06-23 06:53:31,001: DEBUG - ++ ynh_app_setting_get --app=nextcloud --key=user_home
2021-06-23 06:53:31,095: DEBUG - ++ [[ user_home =~ (unprotected|protected|skipped)_ ]]
2021-06-23 06:53:31,096: DEBUG - ++ ynh_app_setting get nextcloud user_home
2021-06-23 06:53:31,350: DEBUG - + user_home=1
2021-06-23 06:53:31,352: DEBUG - ++ ynh_app_setting_get --app=nextcloud --key=phpversion
2021-06-23 06:53:31,446: DEBUG - ++ [[ phpversion =~ (unprotected|protected|skipped)_ ]]
2021-06-23 06:53:31,447: DEBUG - ++ ynh_app_setting get nextcloud phpversion
2021-06-23 06:53:31,700: DEBUG - + phpversion=7.3
2021-06-23 06:53:31,701: DEBUG - ++ ynh_app_setting_get --app=nextcloud --key=fpm_footprint
2021-06-23 06:53:31,807: DEBUG - ++ [[ fpm_footprint =~ (unprotected|protected|skipped)_ ]]
2021-06-23 06:53:31,808: DEBUG - ++ ynh_app_setting get nextcloud fpm_footprint
2021-06-23 06:53:32,092: DEBUG - + fpm_footprint=high
2021-06-23 06:53:32,094: DEBUG - ++ ynh_app_setting_get --app=nextcloud --key=fpm_usage
2021-06-23 06:53:32,189: DEBUG - ++ [[ fpm_usage =~ (unprotected|protected|skipped)_ ]]
2021-06-23 06:53:32,190: DEBUG - ++ ynh_app_setting get nextcloud fpm_usage
2021-06-23 06:53:32,452: DEBUG - + fpm_usage=medium
2021-06-23 06:53:32,454: DEBUG - ++ ynh_check_app_version_changed
2021-06-23 06:53:32,457: DEBUG - ++ local return_value=UPGRADE_APP
2021-06-23 06:53:32,458: DEBUG - ++ '[' UPGRADE_APP == UPGRADE_FULL ']'
2021-06-23 06:53:32,459: DEBUG - ++ '[' UPGRADE_APP == UPGRADE_FORCED ']'
2021-06-23 06:53:32,460: DEBUG - ++ '[' UPGRADE_APP == DOWNGRADE_FORCED ']'
2021-06-23 06:53:32,460: DEBUG - ++ echo UPGRADE_APP
2021-06-23 06:53:32,463: DEBUG - + upgrade_type=UPGRADE_APP
2021-06-23 06:53:32,603: DEBUG - + echo '[+...................] > Ensuring downward compatibility...'
2021-06-23 06:53:32,606: DEBUG - + '[' -z nextcloud ']'
2021-06-23 06:53:32,607: DEBUG - + '[' -z /var/www/nextcloud ']'
2021-06-23 06:53:32,608: INFO - [+...................] > Ensuring downward compatibility...
2021-06-23 06:53:32,610: DEBUG - + ynh_app_setting_delete --app=nextcloud --key=backup_core_only
2021-06-23 06:53:32,736: DEBUG - + [[ backup_core_only =~ (unprotected|skipped|protected)_ ]]
2021-06-23 06:53:32,737: DEBUG - + ynh_app_setting delete nextcloud backup_core_only
2021-06-23 06:53:33,007: DEBUG - + '[' -z high ']'
2021-06-23 06:53:33,008: DEBUG - + '[' -z medium ']'
2021-06-23 06:53:33,009: DEBUG - + '[' -z 7.3 ']'
2021-06-23 06:53:33,218: DEBUG - + echo '[#+++++++++..........] > Backing up the app before upgrading (may take a while)...'
2021-06-23 06:53:33,220: INFO - [#+++++++++..........] > Backing up the app before upgrading (may take a while)...
2021-06-23 06:53:33,225: DEBUG - ++ grep OC_VersionString /var/www/nextcloud/version.php
2021-06-23 06:53:33,225: DEBUG - ++ cut '-d'\''' -f2
2021-06-23 06:53:33,230: DEBUG - + current_version=20.0.8
2021-06-23 06:53:33,231: DEBUG - + current_major_version=20
2021-06-23 06:53:33,232: DEBUG - + '[' 20 -gt 11 ']'
2021-06-23 06:53:33,233: DEBUG - + ynh_app_setting_set --app=nextcloud --key=backup_core_only --value=1
2021-06-23 06:53:33,437: DEBUG - + [[ backup_core_only =~ (unprotected|protected|skipped)_ ]]
2021-06-23 06:53:33,438: DEBUG - + ynh_app_setting set nextcloud backup_core_only 1
2021-06-23 06:53:33,711: DEBUG - + ynh_backup_before_upgrade
2021-06-23 06:53:33,713: DEBUG - + '[' '!' -e /etc/yunohost/apps/nextcloud/scripts/backup ']'
2021-06-23 06:53:33,714: DEBUG - + backup_number=1
2021-06-23 06:53:33,715: DEBUG - + local old_backup_number=2
2021-06-23 06:53:33,716: DEBUG - + local app_bck=nextcloud
2021-06-23 06:53:33,717: DEBUG - + NO_BACKUP_UPGRADE=0
2021-06-23 06:53:33,718: DEBUG - + '[' 0 -eq 0 ']'
2021-06-23 06:53:33,719: DEBUG - + ynh_backup_archive_exists nextcloud-pre-upgrade1
2021-06-23 06:53:33,720: DEBUG - + yunohost backup list --output-as json --quiet
2021-06-23 06:53:33,720: DEBUG - + jq -e --arg archive nextcloud-pre-upgrade1 '.archives | index($archive)'
2021-06-23 06:53:34,689: DEBUG - + backup_number=2
2021-06-23 06:53:34,690: DEBUG - + old_backup_number=1
2021-06-23 06:53:34,691: DEBUG - + BACKUP_CORE_ONLY=1
2021-06-23 06:53:34,692: DEBUG - + yunohost backup create --apps nextcloud --name nextcloud-pre-upgrade2 --debug
2021-06-23 06:53:35,330: DEBUG - 490 initializing base actions map parser for cli
2021-06-23 06:53:35,336: DEBUG - 496 loading actions map namespace 'yunohost'
2021-06-23 06:53:35,344: DEBUG - 504 building parser...
2021-06-23 06:53:35,361: DEBUG - 521 building parser took 0.016s
2021-06-23 06:53:35,366: DEBUG - 526 acquiring lock...
2021-06-23 06:53:35,541: DEBUG - 701 loading python module yunohost.backup took 0.130s
2021-06-23 06:53:35,542: DEBUG - 702 processing action [16789.1]: yunohost.backup.create with args={'name': 'nextcloud-pre-upgrade2', 'description': None, 'output_directory': None, 'methods': None, 'system': None, 'apps': ['nextcloud'], 'dry_run': False}
2021-06-23 06:53:35,623: DEBUG - 783 Collecting files to be backed up for nextcloud...
2021-06-23 08:39:50,275: WARNING - cp: error reading '/etc/yunohost/apps//nextcloud/scripts/app.tar.bz2': Input/output error
2021-06-23 08:40:52,730: WARNING - 6437889 Could not back up nextcloud
2021-06-23 08:40:52,765: DEBUG - 6437925 The operation 'Create a backup archive' could not be completed. Please share the full log of this operation using the command 'yunohost log share 20210623-055335-backup_create' to get help
2021-06-23 08:40:55,529: DEBUG - 6440688 action [16789.1] executed in 6439.985s
2021-06-23 08:40:55,531: WARNING - 6440691 Nothing to save
2021-06-23 08:40:55,702: DEBUG - + '[' 1 -eq 0 ']'
2021-06-23 08:40:55,703: DEBUG - + ynh_die '--message=Backup failed, the upgrade process was aborted.'
2021-06-23 08:40:55,753: DEBUG - + ret_code=1
2021-06-23 08:40:55,755: DEBUG - + echo 'Backup failed, the upgrade process was aborted.'
2021-06-23 08:40:55,755: DEBUG - + exit 1
2021-06-23 08:40:55,756: WARNING - Backup failed, the upgrade process was aborted.
2021-06-23 08:41:27,357: ERROR - Impossible de mettre à jour nextcloud : Une erreur s’est produite durant l’exécution du script de mise à niveau de l’application
Historique
Pour le plantage (systématique) lors de redemande de mise à jour de Nextcloud, je n’ai rien d’autre; Le fichier que me donne le chemin /var/log/yunohost/categories/operation/dantedufixhier … est vide !
encore merci, … à suivre …