Unfortunately I am running into this same error, also migrated with Share-gate tool thought I think it has more to do with the On-premise farm having increased the time out form settings in Central Admin, b/c the On-premise environment form takes 25 to 30 seconds to load. I am wondering was there ever a resolution?
Thus far the only thing I have come up with was to remove all of the data connections being set in the form field default values, this reduces the form load so no time out for new requests. Then I have added a number of buttons next to certain areas in the form for users to update values when editing existing forms, extremely disappointed having to do this as a work around but thus far have found no other way to reduce loads, other than converting them all to HTML5 forms and use CSS, JS/JSOM. Obviously the second solution is time consuming to say the least, especially in a migration scenario...
Definitely would love to hear if you discovered any other work around, suggestions, solutions, and ideas for handling this error.