The issue is very similar to JENKINS-72755

At a jobs page (pipeline with git branches), clicking on "Scan Multibranch Pipeline now" a page shows up "This URL requires POST" and a re-request using POST is required. I have updated to 2.440.2 just now, but the issue was in the previous 2.440.1 also (I updated looking for any available fixes).

The project is within a folder, e.g.

https://example.org/job/FOLDER1/job/FOLDER2/job/PROJECT/build?delay=0 

So far, currently, the workaround is clicking one time more. But I think either the url must be allowed or the button's action is (now) wrong.

Hm.. unfortunately, this is not deterministic. Sometimes it works without an error/message ("Done").