I have this problem with saving playlist. I put one folder with music in my USB drive and make save in this folder - .m3u playlist. After that i tried to open the playlist on other PC and the files doesn't play, because the file locations are different. Is it possible to make playlist and to open after that on other PC?
I use Audacious 3.10.1 on Linux Mint 19.2
What are your "Playlist > Export" settings for Audacious? Did you enable the relative paths option?