the mashup pack seems to not play certain soundtracks for the mashup 

(i do not know the names of the soundtracks but i can try to put them out)

For the nether none of the nether soundtracks play at all

I tried using commands to play certain soundtracks but it did work except they aren’t the Christmas soundtrack but the original instead

The songs in the video are the remixes for the mashup that are supposed to play     

       Christmas nether 1

       Christmas nether 2