I have downloaded songs to my iPhone and when I click on them to start playing, it buffers and doesn't start playing.

Here is some additional info:

• Using an iPhone with iOS version 17.5.1
• All songs imported from Serato
• Connected to Dropbox cloud storage
• All songs that I am trying to play on my iPhone have been downloaded and have pink dots next to them

Why is it taking so long (ie, the songs are buffering and not playing) and in most cases, why aren't the downloaded songs not playing at all?