Thanks Max. I had to be away from this for a few days and keep working on other processor platforms but I did finally uninstall .platformio last night and this morning reloaded that mega2650 project and everything loaded just fine and the build happened quickly.
Of course now, as I go to other platforms, I have to wait while each completely reloads, but I am back to being productive again. Thanks.
I would have liked to get to root cause so I can prevent this from happening again, but from a pragmatic point of view, it is acceptable to be moving forward with real work once again.
As always, thanks for a great set of software.