Ok, I found this previous issue that looked similar.
Got a similar error from the command sudo -u nextcloud php8.1 --define apc.enable_cli=1 occ ldap:check-user admin
Cannot check user existence, because disabled LDAP configurations are present.
Issue was also resolved by forcing an upgrade of Nextcloud:
yunohost app upgrade nextcloud -F
FYI - caldav accounts had been picked up by Fail2Ban & the NC internal threat detection & throttled.
I had to issue the following commands to clean that up before any logins could be attempted:
fail2ban-client set nextcloud unbanip [IP_ADDRESS]
You can retrieve a list of banned (and unbanned) IP’s with the following command:
grep "\[nextcloud\] [BU]" /var/log/fail2ban.log
I whitelisted my home IP by adding the following:
touch /etc/fail2ban/jail.d/yunohost-whitelist.conf && echo -e "[DEFAULT] \n\nignoreip = XXX.XXX.XXX.XXX #<= replace with your ip list, separate with spaces" >> /etc/fail2ban/jail.d/yunohost-whitelist.conf
I also cleared the oc_bruteforce_attempts table in the nextcloud db.
Check entries with the following:
mysql -D nextcloud -e 'SELECT * FROM oc_bruteforce_attempts'
Then remove with a DELETE:
mysql -D nextcloud -e 'DELETE * FROM oc_bruteforce_attempts WHERE ip = "XXX.XXX.XXX.XXX"'