Thanks! Will do when all the rule errors are solved 
Hi @JensH,
sorry for asking back. I found out that it is always seven of these error pairs that occur during startup:
12:00:36.483 [ERROR] [rnal.common.AbstractInvocationHandler] - An error occurred while calling method 'QueryablePersistenceService.query()' on 'org.openhab.persistence.jdbc.internal.JdbcPersistenceService@32829b85': class [B cannot be cast to class java.lang.String ([B and java.lang.String are in module java.base of loader 'bootstrap')
12:00:36.488 [ERROR] [tence.internal.PersistenceManagerImpl] - Exception occurred while querying persistence service 'jdbc': class [B cannot be cast to class java.lang.String ([B and java.lang.String are in module java.base of loader 'bootstrap')
Can I find out in more detail which Items cause these errors?
I had the idea that it could be the empty group items that never receive an update but I have nine groups but only seven errors 
EDIT: I commented out with // all Group definitions in my item files even though the number was higher than the number of errors. Afterwards the error message pairs disappeared … I will monitor that and see if it stays this way …
NO, errors are back after another reboot 
I got those sometimes after an update while restarting openHAB. Bootstrap looks like first initial restore of item values. So maybe a big interpreting the type of sql to the right kind of var.
In my case I decided not to search deeper, because those initial errors don’t see like having any negative impact