Mattermost Impossible to renew certificate

[Vanitarium]

Hiya,
since I have been using Yunohost for a few years now and I am very grateful for this server system: it works very well and during the pandemic Mattermost has helped my family to stay in close contact! Thank you

My diagnosis log is here : https://paste.yunohost.org/raw/ukorusiwah

The Mattermost was updated on the 10/11/2021 and since then the certificate has become invalid and the web admin does not permit me to renew the certificate manually. I do not want to lose all the media and messages by going the route of uninstalling mattermost and restoring it from the backup pre-update.

I need somebody to help me please. Valuable images and messages from my family run the risk to be lost …

[Vanitarium]

I now have a new issue with Mattermost, I tried to backup my data using mmctl which failed saying WARNING: server version doesn't match mmctl version 6.0.0
So I used mattermost command instead as follows:
Can I get around this issue somehow? Thanks if you can help…
Version is 6.0.2~ynh2

mattermost export bulk /home/********/mattermostbackup/bulk_****.json --archive --attachments

That returned this stuff:

FileReader: Unable to get a file reader., unable to open file 20201012/teams/noteam/channels/yqsjxxpt9pbimnaez8jcj7gnda/users/rwkk9ccx5id4x8edx8mapzqk9r/bypuqbqn6ifmbejmcxc8nfjbqh/IMG_0674.jpg: open /home/yunohost.app/mattermost/20201012/teams/noteam/channels/yqsjxxpt9pbimnaez8jcj7gnda/users/rwkk9ccx5id4x8edx8mapzqk9r/bypuqbqn6ifmbejmcxc8nfjbqh/IMG_0674.jpg: no such file or directory
Error: FileReader: Unable to get a file reader., unable to open file 20201012/teams/noteam/channels/yqsjxxpt9pbimnaez8jcj7gnda/users/rwkk9ccx5id4x8edx8mapzqk9r/bypuqbqn6ifmbejmcxc8nfjbqh/IMG_0674.jpg: open /home/yunohost.app/mattermost/20201012/teams/noteam/channels/yqsjxxpt9pbimnaez8jcj7gnda/users/rwkk9ccx5id4x8edx8mapzqk9r/bypuqbqn6ifmbejmcxc8nfjbqh/IMG_0674.jpg: no such file or directory

So, I now do not know if all the attachments have been stored or not.

2. Mattermost stopped working and the log can be found here:
   https://paste.yunohost.org/wuvaqitoru

Can anybody help with this??
Do I need to reinstall mattermost?
Can I restore it from an earlier backup and then restore my data?
Will I lose my data?
I just do not know enough about these issues and why I lost the connections to mattermost server?
Thank you if you can help.