Now 3 years later I have the problem with Prestashop 1.7.6.8 ! Also appeared after upgrade. It seems to be a continuation of the problem from 1.6.0.11 already, as reported by so many and solved in this long thread that I read in its entirety:
I too have the problem with saving products, namely that it takes often about one minute and longer for the process to complete.
Strangely, when I leave the page from lack of patience and return, the changes seem to be saved. However the process of confirming the saving of the changes and reloading the product editing page or the save button has apparently some problem. Sometimes the problem doesn't appear but most often loading circle keeps spinning and save button stays grey for long, if not forever. The behavior is quite random but most often it goes as described, roughly one minute time to save and load the catalogue if that is what I clicked to do - if I click on just "save" then I am not even sure whether the changes were saved as nothing seems happening.
Deleting cache didn't work and changing browser either.
Unfortunately I am neither coder nor technician, so any suggestions must try my technician and programmer. I just wonder how is it possible that problem that appeared already in 1.5 or 1.6 keeps returning, even after I saw someone finding a bad ajax use as the source of the problems.