This is quite frustrating issue which has made some BackOffice users mad for sure.
The product page is saved sometimes, sometimes not. It may work on one browser but fail on another one.
Read more to see one of possible solutions of this problem.
This is what worked for me, when product save failed on Chrome, but always worked on Fifefox.
Near 252 line find and remove
submitHandler: function(form) { form.submit(); },
Save file, refresh product page and it should work.
If you know any possible solutions please share them in the comment section – thanks.