Here we go again...
I don't want to polemicise but with Survey123 happen too often that I have to try to find a way to solve an issue and the error messages never help.
So, This time I am simply trying to "create sample template" and I get this error message.. couldn't find this error and it doesn't mean anything.
Did you create the survey with Connect? Can you share it's Excel design file? Maybe there's a reserve keyword lurking somewhere.