Please lose the use of bold formatting when seeking help.

First off, tracker and its own provided binaries has nothing to do with gpx files. Those gpx files are related to GPS co-ordinates/pinpointing, etc. Read this for more information as to what proper trackerd actually stores and doesn't store, what filenames it uses or it doesn't use.

There is a nifty trackerd configuration tool known as tracker-cfg. From there you can read all the relevant information and control trackerd in a way that you want it to operate.

In default/most cases, trackerd keeps its own log in: "/home/user/.local/share/tracker/trackerd.log". A simple:
will give you what files does trackerd has access to and more. If the logs within "/home/user/.local/share/tracker/trackerd.log" is not enough then use tracker-cfg to increase the verbosity of the trackerd output when trackerd does its own rounds.

When issuing: you will need to give trackerd time to re-initialise again and generate the database in which stock media player for instance depends on. You can always check in a couple of ways: 1) through the log as mentioned above, 2) starting up media player (and it should show you a banner that it is retrieving information on files, etc 3) Using things such as cpumem-applet and monitoring until the first of the two bars goes down and stays down.

Depending on how big your list of media stuff and how you configured trackerd the results can vary. If, for whatever reason you do not get a full list of media (as you expected) or that it still shows no media files. You may have a more serious problem: may show you issues if and when they occur.

Judging from your various outputs, you would have realised to also have sysklogd installed and therefore /var/log/syslog would show you information pertaining of and on more of userland tools rather than at kernel level information. If you're not familiar with all of what I'm saying, I do not understand why you have CSSU-Testing/CSSU-Thumb installed knowing full well that they are not there for the average users.

If the issue started happening a month ago, you should have tried to look into it as soon as you can before you forget what you did last and/or installed something else which may ruin even more your setup.

If you have no recollection of what you did last to make your setup become like this and you don't have any decent explanation why you have CSSU-Testing/CSSU-Thumb installed/enabled when you aren't even familiar with basic linux commands then I only offer one suggestion. Backup and re-flash, it will be a lot simpler than trying to finding a needle in the haystack and to have people stabbing in the dark.