Hi,
Which version of DFFS are you running? – I did have a problem in an earlier version where trying to save the form and receiving a validation error on for example a hyperlink field where you used a to long URL. In this case, you would not be able to save the form after correcting the URL.
Regarding the save to localstorage:
I don’t have anything ready, but it could be done. I do however think that there must be a reason for this behavior and think you should investigate it a bit first.
If you are able to recreate it, you must hit F12 and look at the console when it happens – you will most likely find a clue there.
Alexander