I just switched from PhpED 6 and now I'm running PhpED 9, I'm using the same project so everything is still mapped properly. After I finish a debug I get files and tabs like "Filename.php____jb_old____1".

This never happened in 6, before it'd just keep the tab of what file you were actually on but now it's these temp files or whatever they are. How do I
disable this / fix this so these files stop appearing?

PhpED does never create anything like that.
Moreoever, v9 is a very old version, not sure where you obtained it from.

It was the last version we had a license for. All I know is that when I switched from 6 to 9 it started to create those files after debugging so it has to be PhpED.

Again, PhpED does not do that. Check your other applications, including php code you run.

Files with those sorts of names are created by JetBrains products (thus the _jb_)