When I delete a backup from the browser GUI, it never goes away. Its still there in the GUI even after a restart.
What Duplicati version, and if you’ve recently changed, do you know if prior version (what?) had the issue?
Please give the exact steps you follow. If you need to, you can create a new backup just to test its deletion.
What operating system, what browser? Have you tried a hard refresh on the browser, or tried some other?