I'd like to help you fix this, NeinFrankenstein.
Let's start by updating your QuickBooks Desktop by following the steps in this article: Update QuickBooks Desktop to the latest release.
After restarting your computer, go to the Payments to Deposit window and try to sort the payments. If it doesn't work, we can do the Verify and Rebuild Data.
Here's an article for the step by step instructions: Verify and Rebuild Data in QuickBooks Desktop.
Once done, sort the payments again.
Please let me know how it goes and I'll get back to you as soon as I can. Thanks.