Had to engage Support to remove all Holiday records, then re-added them manually. As of now, this appears to be working again.
Support says they have no idea why this happened and another server in the same country with the same exact holidays has no issues. When I re-entered the holidays I only used A-Z, a-z and 0-9 avoiding all special characters. No idea if that will help. but that's what I did as an FYI.