probably you would need to check the whole chain
Can you check following
ls -la /var/lib
Usually folder influxdb should be linked to /mnt/dietpi_userdata/influxdb. And within /mnt/dietpi_userdata/influxdb all files and folder should belong to user & group influxdb
AAAHhh and now I remember Influxdb not working after update - #6 by Joulinar
Thats why a forum search could help sometimes