After entering an end date for an income series, I click "Update" and an error appears in the bottom-left of the screen saying "Sorry, but we were unable to make your changes." If I then check my Spending Plan in a month after the end date I entered, I still see the series. So it looks like the end date really didn't take affect. Interestingly, if I go back to edit the series again, the end date does appear as I entered it.
I've noticed that if I refresh the browser tab after seeing the end date in the series, the end date goes back to being blank. So maybe seeing the end date after the error is just some browser caching, while the back end had an error resulting in the data for the new end date not being saved.
I'm using Firefox version 133.0 on Fedora Linux 41.
I was able to workaround this by setting the end date in the mobile app.
Let me know if you need any more information.
Thank you.