Openhabian OH 4 - Trendline (for most items) not working anymore after update from 3.4

Hi,

i recently updated to Openhabian OH 4.
I noticed that the Trendline (for most items) is not working anymore.
In other threads I read that the persistence service rrd4j should be checked. It was off, so I enabled it.
Also found that all log files seem to be available here (I see for each item a file).
openhabian@openhabian:/srv/openhab-userdata/persistence/rrd4j

What can I do to fix it?

Regards,
Thomas

solved, but this will delete all historical data! I just deleted all files in the rrd4j. OH created new working files automatically

Today I rebooted the system and most trends are not working anymore. The “working” trends do hold the data only from the time of teh restart (last 4 days are lost).
What could cause this? How can I fix this?

Greetings Scotty.