Try disabling the Soundtrack Menu and the Music Mod Callback mods. They are sadly outdated and not compatible with any mods that use Stage API to add custom floors.

Unfortunately @Guwahavel I have removed those and am still experiencing the issue. And it's happening with The Future mod, too.
The only music mods that I have right now are Excelsior (which is SUPPOSED to be compatible with both), and Uninterrupted Void Music (which shouldn't effect anything here). I've even tried turning off Excelsior while in the Grotto before, closing and reopening the game to do so, and, uh, not only did it not fix the issue, besides changing the music, it also caused every single room to turn empty.

I don't know what's causing it and it is really frustrating me. Help. I want to experience the complete music even without Excelsior.

...I finally managed to get the Boiler again, and the issue is the same there.

Originally posted by Holly:

Unfortunately @Guwahavel I have removed those and am still experiencing the issue. And it's happening with The Future mod, too.
The only music mods that I have right now are Excelsior (which is SUPPOSED to be compatible with both), and Uninterrupted Void Music (which shouldn't effect anything here). I've even tried turning off Excelsior while in the Grotto before, closing and reopening the game to do so, and, uh, not only did it not fix the issue, besides changing the music, it also caused every single room to turn empty.

I don't know what's causing it and it is really frustrating me. Help. I want to experience the complete music even without Excelsior.

I had this issue with Godmode Achieved, try disabling Uninterrupted Void Music

hey im getting this too but i have non of the mods stated before and its still restarting the music per room