Hello, maiken,

I hope you are having a good day, and welcome to the Community! I am happy to help you. With this being a sticky setting, there could be several causes for the number to change, like editing a previous transaction number or entering transactions while the forms are being created.

In the meantime, to rule out data damage issues, let's go ahead and run a rebuild and verify. Go to File, Utilities, then Rebuild Data. After that process, run the verify tool, which can be found by doing the same steps as mentioned by selecting Verify Data instead.

This article is very resourceful for more information about verifying and rebuilding data in QuickBooks Desktop.

Let me know if you have any more questions! My team and I are eager to assist! Take care.