Design tab emty after 6.1

Hi,
some time ago i created a quite large form (editing would fail in 50% of cases due to server timeout even) and i would like not to do it from scratch again. Thing is, after 6.1 the design tab is empty, setup is ok. It would not be a problem if database save didnt check this to determine columns for saving. Which there are none, so only id, date, etc are saved. It even managed to edit the table retrospectively and delete all other columns with data. Strange thing is that whole form still works right. So it looks like this:
Form is populated, validated and sent
Admin and customer gets emails with all the data
New row is inserted into database with no data, nor any columns for them exists
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Is there any way to repair this behavior? Any idea will help here
Thanks in advance

I should also add, that now form edit load time is instant, so its not just visual bug, its not loading designer part at all

Did you convert the form to v6.1 or this just happened after the update ?
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usually there should be no problem, try to create a form copy, does it have the same issue ?
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Best regards

It was caused by update itself. I tried to convert it later, but result was the same. Any copies or backups didnt solve it either.
Did you encounter this ever before or its just some rare bug without any real possibility to solve?

No other users reported this issue before as far as i know, can you send me a backup of the form using the contact page ?