There's got to be a simple explanation for all this. From everything I've read, I think either:
1. There were one or more revisions to the FDCM over the years and the flash is not compatible with all of them.
2. The FDCM and/or actuator was already failed, or getting ready to fail, before the person went in for the flash and the flash exacerbated the issue.
3. The dealer did the flash incorrectly and can't fix it because they don't know what the heck they're doing.
Sadly, #3 probably happens more often than the others! Glad I apparently got lucky. I feel for those who didn't.
2010 Brilliant Black Crystal Pearl Coat Grand Cherokee S-Limited with various bits 'n pieces... broken in but not even finished!