every thing you discuss here is work fetch only.

Resource Scheduling is what task to run, and how long to run it. If you have TSI set to the default of 1 hour that means that BOINC will likely change its mind on what task to run. and so that may be the source of some of what you are seeing.

I set my TSI to 720 so that it is 12 hours and tasks run to completion unless they take longer than 12 hours to complete at which point they may be switched out.

that's the other story..

i'm running @ 600 - CPU-tasks are all under 3 hours for the longest, deadlines are all several days away. so it should not switch anything.
6.6.28 does no longer try to juggle everything around every other second, but it still does it from time to time.

anyway - shutdown time, going on vacation..

Yeah, I saw that and lost the message log because of another issue - so I am still on the hunt for a clear example of the instability ...