I’ve checked that if you leave the seed field untouched, there isn’t any issue. But if you touch it, even if you delete everything in the seed field, you won’t get reed of the error message. Even if you uncheck Randomize, it will persist.
Downloading the XLSForm, I see that the field parameter remains with a randomize=false;seed= , or randomize=true;seed= , it doesn’t matter.
Obviously, deleting the ;seed= from the string and uploading the XLSForm would solve the problem, but non-advanced users would have this a difficult thing, and it’s not the purpose of the Kobo Toolbox to force users to go through that. It’s clearly a bug that should be corrected.
In the mean time, I have to tell non-advanced users to simply delete the problematic question(s) and recreate them again.