Not sure if this is really practical, but would it be possible to do a check that we’re not submitting an ACF Form that will exceed the max_input_vars, and if so throw a warning and stop the form from submitting?
It could be a simple count of the number of fields (bonus points if you could get other fields on the page as well outside of ACF) to see if we’d be hitting that limit. I know it might not be possible to get an exact count (I think cookies are counted in the total for example), but close would be nice.
I just hit the limit in the ACF Field editor, which caused me to lose the last field, which happened to be a repeater. It’s not the end of the world when you lose a normal field since get_field should still be able to retrieve the value, but I think with a Repeater it checks back to the original field, which was gone. Oddly enough once I finally managed to increase the limit and recreate the field, the content didn’t reappear on the front page. I had to go into the post and hit save for it to show up, even though when editing the post I could see the content.
I think the number of fields was 47 if that helps.