I switched off randomization for the subquestions to better test (but it also showed when it was on):

 

Here you see it. Tested on LS 3 Version 3.27.18+210921

 

I don't think the problem is the platform...

I have to admit that I’m really confused. When I programmed the sub questions they were not labeled that way.
And more : on the developper section for subquestions, the number 89014 does not appear.
I’ll gladly admit that I’m no LS expert but the disappearance of a subquestion in the developer mode, then it’s reappearance when duplicated in another survey or when in preview mode.
Perhaps you can explain, for preventing further stressful experiences.
This could be related to the version I’m using?
Anyways thanks for everything

If you say you did not enter these strange codes initially, so you will have copied something or clicked twice when entering the subquestions (maybe in quick-add)
Something like that.
Now there are double codes and LimeSurvey renames to these 89012 codes or whatever.
The best to get rid of it. Remove the question and create it again .

Joffm

I don't know if it is related to the version you are using, but it could be. We would need to look at the release notes for all versions after your version to see if a bug that fits the description has been fixed. But your version is now over 12 months old, there could be a potentially lot of versions in between and a lot of bugs being fixed. This is not a bug I had ever heard of, but that doesn't mean anything, it could be introduced in one version and immediately being fixed in the next one.

Sometimes, the survey is corrupted (for whatever reason), did you do an integrity check? (Configuration --> Check data integrity - You might not have the rights to do so, if you are on a university installation, for example).

You can have a look at the survey logic file to see if you can see something strange and if the item is shown there.

And sometimes, if a survey is corrupted, it helps to export and import it again. Give it a try.

Or like Joffm said, try to create the question from scratch and see what happens.