Hi,
I noticed the same thing after updating and thereby restarting the container. The problem was that /var/lib/influxdb2 in the container was not mapped to a path on the host. This path is new in addition to /var/lib/influxdb. See Upgrade Example - Minimal here for example.
To fix it add a path like this
Container Path: /var/lib/influxdb2
Host Path: /mnt/user/appdata/influxdb2