I have being using plexamp on my mac (IOS 10.13.4) and it was working perfectly, then installed the new security upgrade from apple (2018-001) and plexamp has stopped working. Its connecting to my PMS, showing all my music in the discovery window, but when I select anything (song/radio station/album) nothing happens. The play/pause button doesn't come up, it just sits there.
I have tried simply uninstalling & reinstalling by sending app to trash. There didn't appear to be any residual files in the logs or caches, but when I reinstalled it automatically picked up my PMS, so I don't think I uninstalled it correctly. Looking at the forum, for a winows machine, there is a folder in the local folder (see below) but I can't see the ios equivalent.