SharePoint Lists: Renamed Lists and Columns are not displayed with new names

Hi all,

I have found quite some posts here around the same problem. The most promising one seems to be this one: https://techcommunity.microsoft.com/t5/sharepoint/renaming-columns-gt-new-name-not-showing-for-site-members/m-p/3856317/highlight/true#M72110

I have added my symptom of said problem into that thread. Basically, I create lists and columns by default without blanks and special characters, then later rename them with blanks and characters. First to make it easier for the computer eye, second to make it easier for the human eye. Never had an issue there until recently, when all renamings are somehow working but not displayed.

Now I stumbled upon an interesting behavior, that justified a new thread in my regard:

So while problem solving, I created a new list from an existing list (the buggy one). That was obviously not working and I got the same wrongly displayed column names. But now  I found an interesting new facet to this:

When opening the list setting and trying to rename the columns from there, my title column isn´t showing. I was wondering already on the initial list, that there was not "edit" in context menu anymore, but I could do this via list settings. Now when I go there in the new list, it is just not there. Nothing to click on.

Please help.