Man, what perfect timing. I too am having this problem! It started yesterday when I attempted to add a Note field to my survey. A field that requires NO user input, yet wants to create a new field in the survey database. I've added fields to this survey using Survey123 Connect before, but attempting to add this one results in the same error Mike is getting. If I remove the Note field I've added, the error goes away.
According to other answers I've seen elsewhere I've chosen Save As... in my spreadsheet and given it a different name in a different location. Then using Survey123 Connect to open that new spreadsheet, I was able to publish and generate a new survey. This works, even with the offending Note field. But this is definitely NOT a preferred method. It doesn't retain any submitted surveys, if you're modifying a production survey (which you probably shouldn't be doing anyway) and it breaks any maps or views that you may have created to analyze data from the original survey. (Not to mention anything that relied on webhooks from the original survey, which now has to be recreated in the new survey...)
It still boggles my mind that there are two products to create surveys for Survey123 and they are not compatible. The moment you touch a survey with Survey123 Connect, you can no longer use the web based survey editor. These two things should be cross compatible. This needs to be fixed. It's not a feature, it's a bug.
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Roger Asbury
Analyst/Programmer - Fairbanks North Star Borough