Hi
There’s a strange issue in 10.5 which happens randomly when opening saved projects.
Activated channel strip EQ on groups might cause them to be muted when engaged, the only solution is to disable the eq or duplicate the group and re-route everything again, and the same eq will work fine.
And on some audio tracks activated eq might mute just the left channel, same solution, disabling the eq or duplicating the track to fix it.
Using -
Macbook Pro 16-inch 2019
Catalina 10.15.5