Duplicate requests after chrome update to Version 75.0.3770.80 (Official Build) (64-bit) and save data twice into database issue

I think I've found that this is related to preventDefault... looks to me like Chrome 75 is terminating a formPost if made via JS if you don't do a preventDefault() on the original event.

check, if the submit button has the type "submit" or "button". If your ajax is submitting the form, then the html button should have the type "button", otherwise both is submitted. I think that has solved the problem for me.