From https://translatewiki.net/wiki/Thread:Support/AJAX_editiing_hides_error_message_when_edits_were_not_saved:
About 5 to 7 percent of the times when I hit the "save translation" link or button in the AJAX editor, saving fails, and a newly added error message is shown in the page. But at the same time, the page is scrolled up a bit to a position where the error message is just outside the visible area (viewport). As a result, I never know about the error unless at the end of a session, I scroll through the entire page so as to control, if all went well. Since that often takes very long, and since Mozilla and other browsers usually crash after a while due to the memory leaks (which I assume are part of JavaScript libraries), I often loose a part of the edits made with AJAX editing.

Ideas of remedies:

Do not scroll the dynamic status/error message to become invisible.
    Scroll back to failing message when an error is detected.
Give an audible feedback (similar to cash registers in supermarkets) of success/failure.
    Given an audible feedback only on failure.
    Let users select audio files to be played, including none, for both cases.
Alter something sufficiently visible when an error is detected, such as overall background color, etc.

This seems like a valid issue that users would encounter somewhat frequently when errors do occur so noting this here so that it doesn't get lost.