Random instrument slots suddenly disabled

I often use the first couple of vst slots for bass and drums plugins. The past few days, I’ve been in several projects where slot 3 was disabled. I tried 4 and 5, also disabled.

This is occurring on all the projects I open. After some random clicking around what I discovered is that 1 and 2 work, 4, 5 and 6 are disabled, 7 works, 8 is disabled, and then several after that work (haven’t checked all 64).

Thinking I must have somehow corrupted the projects, I tried creating a new blank project and got the same results.

I’m getting the exact same behavior on two different computers. Have any of you encountered this sort of problem and if so, what was the cause / solution? Would be grateful for any insights.