Rebase button in the MR takes a while to properly become disabled after being used

When using the fast-forward merge flow (https://docs.gitlab.com/ee/user/project/merge_requests/fast_forward_merge.html), a "Rebase" button appears in the MR's UI if the MR is behind the main branch. This button, however, is buggy. When we click it, it spins for a few dozen seconds and then it appears again (even if nothing was pushed to the main branch during this time). Then, if we wait a few minutes and refresh the page, the button is gone and the MR appears as rebased.

GitLab version: 14.1.3. I am in the process of testing this in the latest version as well and will report here soon.