Still having this issue, I searched and searched online yet again, and one thing suggested was turning off online AI. I switched to offline AI and was able to complete a flight finally. Also, it was suggested to try a different flight plan on Simbrief than the one they give first. (most common or something like that). I'll try that next.
But after one session, the online AI seemed to be the culprit. For now, of course. More testing is needed, but for now, it's given me something to try other than reinstallation....