When I try to create a new question (simple List yes/no), the Question Code shows up with a red X.

I know that you get a red X if you try to create a Question Code that is too long (too many characters) or if you try to create a Question Code that is already used elsewhere in the survey. Both of these situations have a pop up error message telling you immediately what the problem is.

However, in this case (see attached JPG), there is an obvious error but no indication of why.

If I run a logic check on the Group, it shows no logical errors.

Once the red X shows up in the Question Code I can still edit the question but none of the changes will be saved upon clicking Save.

Version 4.1.16+200407
Running on Windows 10/Firefox browser version 75.0 (64 bit)

Copy the survey and see what happens in the new survey.

Something like that : bugs.limesurvey.org/view.php?id=15871

I can not reproduce on 4.1.18, but have it in 4.1.3

Tried copying the survey and opening the new survey. The question that previously had the red X is still showing this as an error. I cannot edit or change the question.

OK, so this didn't help. Sometimes there is something stuck in the survey (deleted or moved questions, etc.) and with copying it might loose the problem.

Denis says that he can't reproduce the problem in the latest version, maybe you need to make an update?

Also, export the survey and import it again. And maybe post it here. So we can import it and have a look ourselves.

I exported the survey (to *.lss file) and imported it to a new survey. The Red X is still showing for the question code.

A copy of the survey file (.lss) is attached

I can reproduce in 4.1.16.

New bug reported - bugs.limesurvey.org/view.php?id=16162