I have the same disappearing problem. I put the tag in the Content section, have to fight with it by manually adding square brackets (even if I copy and paste the line in, Visual editor deletes the square brackets every single time)

Then I go to view and everything is perfect.

Then if I go back to edit mode, the tag code lines are now invisible. They are still there, but you cannot see or edit them.

If you go back to view the lists are still there

But if I make any change in the document at all, like adding in one word to text content, when I go back to view the lists are completely gone.

The workaround I have been using is to change any list pages back to WYSIWYG in which tagging lists work perfectly.

I have the same thing happening. I can make a tagged list as per this article https://www.worldanvil.com/learn/bbcode-tutorials/tagged-lists and when I view the page it works fine. If I move away from the editing page and go back, the tagged part is gone. I have redone it multiple times and it gets deleted every time