We identified an issue in combination with memory expansion cards that use the MCA feature Matched Memory Cycle. Most memory cards use this feature for optimal transfer speed.
The issue appears when data is read from the OPL2 and randomly locks up communication with the card. To revive operation a power cycle is required.
Usually one would consider that the OPL2 is not used much with reading from it because playing music is mostly writing data.
Though the OPL2 is slow and requires delay after writing the address byte and after writing the data byte. The standard way for an ISA card that also the example music player uses on the Adlib disk is
6 dummy port reads after writing the address and 35 dummy port reads after writing data.
Basically every game/application that has Adlib support uses that approach as well.
My testing shows that the communication often get borked when starting a game and the code tries to detect an OPL2. When the a game runs it seems to work without failing intermittently.
Without extensive statistics I tried on Commander Keen 4 and on the 6th start the card went silent.
Some games seem to hit the issue always on startup like Legend of Kyrandia, which stayed always silent.
The problem is gone as soon as the memory expansion card is removed.
TubeTimeUS knows about the issue and I sent him also the test programs I wrote.
Maybe someone lives close and can borrow him a Model 80 for testing?