by Andrew Normore.
Hello everyone, and thank you SO MUCH for your assistance.
It has been the entire weekend, and two work days, with out any reports of incident!
It appears that using individual database accounts has solved the issue. So in a way, this is sort of related to caching, which makes sense. I think some inserts were being triggered from other sites, that HAPPEN to have matching ID's in some SQL statements. This is why we cannot reproduce the bug.
So if you just follow STANDARD MOODLE INSTALL INSTRUCTIONS you can avoid problems like this.
... and now we know.
I'll report back if we are still experiencing problems, cheers, and thank you again!