I'm encountering the error " open activities with no group ID" in the logs. After investigating, I found that it originates from an out-of-the-box Guidewire batch process in PolicyCenter called Team Screens. Unfortunately, I don't have access to the source code since it's OOTB. I've already validated that the Activity.AssignedGroup is not null, but I'm trying to understand why this result is occurring. Any assistance would be greatly appreciated!
It will be a little hard for anyone to pinpoint your issue. You may want try assigning the activity to a different group and see if you still get the error. I think that this batch process posts this log message once and will say "Found X open activities with no group ID" for the total number of activities in with a null group ID. Are you saying you checked every open activity in PC and all have a non-null groupID?
This KB article seems to indicate that the groupID must be null for this error to occur. Login required for this link.
https://partner.guidewire.com/s/article/What-statistics-does-Team-Screens-batch-process-create