Occasionally, we get a warning "Mailing has not been saved, Content maybe out of date, please refresh the page and try again" when trying to save a Mosaico mailing." The mailing does not save and any changes are lost. When this happens, it seems to happen for everyone and every mailing. This also prevents a test email from being sent, presumably because the mailing can't be saved.
Cleanup caches seems to fix this problem, but not before whatever changes the user has inputted are lost and hair is torn out, tears are shed, etc.
Nothing is logged when this happens. I have been seeing this for quite a while, at least since 4.X. Here is a past question about what sounds like a similar issue.
Is there anything to be done to fix avoid this in the future? Anyone have any idea what the problem may be?