Compared all the scanning settings, results below:

MM5 Installed & MM5 Portable had the same scanning settings.

MM4 had a couple of differences, Infer Properties and Scan Folders for Artwork were both checked. These were not checked in the MM5 settings. (Now also Unchecked in MM4)

MM5 had Analyze Files for Duplicates checked and MM4 did not have this checked. (Now Also checked in MM4)

MM4 should have also had this set, but at some point I must have unchecked it? I've been doing some house cleaning in the Library and had been fiddling a bit with the settings between versions while cleaning up.

They are now all set the same. Also checked the scanned directories and they were the same across all MM versions.

Maybe scanning settings differ?

Yes, both running at the same time and both have folder monitoring enabled for the same folders.

Also, have the same setup for the MM2024 portable version as for the installed MM2024 version.

Are they both running at the same time and do either (or both) have Folder Monitoring enabled?

Using MM4 4.1.31.1919 and MM2024.2.0.3162 (both gold lifetime), with Windows 11 Pro up to date.

Running both installed (non-debug or debug) versions of MM4 and MM2024 at the same time, I was having some problems with MM2024, but few if any problems with MM4. The exception being MM2024 locking up sometimes causes MM4 to also shut down. MM2024 was VERY slow at saving edits of multiple track properties. While trying to complete the saves, it was almost impossible to do anything else it was so sluggish.

Decided to try MM2024 in portable mode and what an amazing difference it made! So far MM2024 is MUCH faster and is working a LOT better, also seems much more stable. I just copied the MM5.DB, Mediamonkey.ini and persistent.json files from the installed version of MM2024 to the portable directory and it just worked just like the installed version.

I'm not sure if there is something wrong with my installed version of MM2024, it has a conflict with MM4 or exactly what was causing problems when running both installed versions, but the protable version made a HUGE difference. Recently new PC, which I was starting to suspect, but MM4 and now MM2024 portable work just fine, making the hardware much less suspect.

Also, should the installed version of MM2024 be uninstalled and just continue on with portable? Or should I completely uninstall and reinstall MM2024 as an attempt to fix the problems? Due to Zvezdan's RegExp add-on, which I just can't do without, uninstalling MM4 is just not an option.

Thanks for any comments or suggestions!