So I don't really know where to post this? I contacted support for this issue and from what I could tell the issue was recreated but I wanted to try and see if many others could recreate this problem and also try and get a fix for it.
So basically TS4 to my knowledge does not play custom music properly at all in some cases.
All my music up to now has the required Kbps. I believe mine are typically 192 If I'm being very specific.
But anyway, point is all my tracks are perfect to work on the game and yes they are .Mp3.
However I have 800+ tracks, and no, that's also not the issue, I did test this a bit further.
On the tween radio station if you place custom tracks no matter what you do, they wont play. Other radio stations do this too, but not to every track, its simply inconsistent. I removed all my music and placed 35 tracks in tween and non of it would play at all.
Afterwards I realised that the one radio station that has always worked for me was "Alternative", I stuck all my tween tracks on to alternative and guess what?
Every single track could work, or at least the radio didn't stop playing as many custom tracks that it could.
Essentially the game from what I can tell has issues with the radio stations (some) not playing tracks and having a bug of some sort.
I haven't tested every single station but I can definitely say more than one has issues.
The only one from my experience that I can confirm is definitely fully working is "Alternative". Throw what you want at it so long as it meets requirements and it works.
Note: I did this with no CC and a clean install and I did it with my CC afterwards. The game does definitely has some problem playing music if it works on one station but not the other. I've ran a repair multiple times etc. All my tracks meet the requirements and they only work on some stations, the game has an internal issue that needs to be fixed the game will play music so long as it was added by an EP etc, its specifically custom music. Unless someone else knows what this is, I ask anyone else to recreate this.