When I tried playing stuff yesterday, A+ would work for 3 minutes, then silence, appeared to still play. Didn’t matter the content. Restarting A+ would reset the 3 minutes, then same.
Surely not a license problem 
You can try deleting your Audirvana prefereces, maybe something got corrupted somewhere…
Close Audirvana.
Apple hide the Home Folder in User Library at some time depending on OS System… When you have clicked your Home Folder, and cannot see the Library Folder in there,
just do a ‘‘cmd J’’ to show the folder settings preferences and see at the bottom… click Show Library Folder and then you’ll have access to the rest forever.
Go to User… Home Folder… Library… Preferences…
trash com.audirvana.Audirvana-Plus.plist and com.audirvana.Audirvana.plist in that folder (those are A+ software preferences, back them up or not)
Restart MAC. Restart Audirvana, You’ll need your serial number i think.
Choose your preferences again in Audirvana menu and audio settings menu,
then see