THANKS to the great support I got from NextGen, the site is fixed, running WP 9 + latest NextGen and also NextGen Pro. After trying a few suggestions from the exceedingly helpful Erick, their developer looked at it and fixed it.
Here is what I learned about the issue: When all else fails, use the RESET button at Gallery > Other Options > Misc. > Reset
That should solve any issues, although you will have to reset any default options that you changed. If this does not work, then email NextGen and they will run a test and possibly a different reset function.
NOTE: Clicking RESET does not affect the galleries, images or gallery displays. It restores NextGen settings to default values and should fix any outstanding errors.
The explanation: Developer re-upgraded NextGen to 2.0.65 and ran a reset tool to reset all the settings including visible settings in the options panel + non-visible database settings. Then he did a reset on my site to re-adjust global settings to what they were prior to the reset. There was a corruption in the database for unknown reasons, so he made adjustments to the reset functionality, then reset the options to match the server and domain.