Documents to not export with same file name after updating to InDesign 21.2

Also, in my experience, if you change the name during export at some time, that name sticks, so it should be exporting with the same name it used at the last export.

When you open a file created in an earlier version, do you see the word Converted on the tab bar, next to the file name? 

     This indicates that the file was created in an earlier version of InDesign (v20 or earlier) and it has been converted to the current version of InDesign. It also means that when you choose File > Save, it’s as if you chose File > Save as and you have to choose a name and location for the file. If you choose the original name and location, then you’ll get a message about overwriting that file.
     This is a feature, not a bug because once the file was converted to a new version, it was not easy for the older versions to open the back up again if you need to return to them. These days it’s a bit easier, but this procedure has been in place forever as a protective mechanism. 

What’s your operating system version?

Also, can you please elaborate on what exactly happens: does the file name change when exporting the same document? If so, then what does the file name change to? Or is it something else? Any screenshots would be helpful.