I ran into the same problem after updating to 7.9.2.231 . Apparently this is a known bug and they're working on fixing it.

In the meantime the "fix" is to click the "Force Full Backup" option next to your problematic backup job. Which admittedly is not the greatest "fix" since you're having to upload your entire backup set again. But it does get rid of the error. Here's to hoping it doesn't happen again.