I have an old desktop I use for Win9x games from time to time and decided to copy over XMPlay to have some music on there whenever I'm doing stuff with it. Works great for individual file playback and just being able to click and play files, but it appears the library functionality is currently broken.
When I add a folder to the XMPlay library it works as normal when sub-dir scanning is disabled, however as soon as I check off "Sub-folders" for that entry in the library the Entries column switches from showing the number of files in the directory to simply saying "miss". Weirder yet, even if I manually add files from that folder from the playlist using "Add to library", as soon as I rescan the library after adding those songs they get removed from the library and I'm left with zero entries again. I've tried this on my actual Windows 98 desktop as well as in a virtual machine and get the same results for each.
I had noticed this with an older version from 2019 and also updating to the latest version now. I'm going to try a few older versions of XMPlay and see if anything there changes.
Edit: From testing various versions on the site, it appears the last version where sub-directory scanning works on Windows 98 is version 3.4.2.1. Version 3.5 and later all seem to just "miss" the directories as soon as you enable sub-directory scanning. This is a little unfortunate as most input plugins don't seem support anything earlier than 3.8 anymore.