I have a datasource configured on InfluxDB, and today it was entirely bugged in the Grafana app (somehow missing, and somehow still there, Schrodinger's datasource)

After looking at logs, I found the root cause: an update on the influx's grafana plugin.
The application tries to update its plugins on start-up which seems to be located in /app/code/data/plugins-bundled/, which is read-only. Therefore it could not finish the update and never loads the plugin.

Updating plugin  pluginId=influxdb from=13.1.3 to=13.1.6
Failed to install plugin  pluginId=influxdb error="unlinkat /app/code/data/plugins-bundled/influxdb: read-only file system"
plugin process exited  logger=plugin.influxdb

This only happened now because there was an update published yesterday on the Cloudron package, which made the container restart.

Adding this to /app/data/custom.ini "solves" the problem:

[plugins]
preinstall_auto_update = false

But correct fixing would be putting plugins somewhere in /app/data or make their directory writable by the update process.