I could see AppMon server log has the following these lines quite often. what is causing this issue, is it dashboard. I have verified the Dashboard Custom_Mem_CPU_Thread dashboard as well which is populating data without any issues.
Data source is properly configured, Filter is selected for last one hour etc.,
I'm wondering if you have a report scheduled to be generated every 2 hrs, but it's not really complete so nothing can be generated. Go into the "Custom_Mem_CPU_Thread" & "Custom_Database" dashboards and see if there's a report scheduled to be run. I'd be willing to guess that someone saved these dashboards without really wanting to save them. Simply deleting the dashboard would also resolve this issue, assuming the dashboards are not of any value.