Blown tube

Just noted that you said your amp is self biasing --FWIW I've a self biasing amp - put in a new set of tubes and one tube's plates started to glow red. Changed it out thinking it might just be the tube, the next tube also glowed red. Returned the amp to the manufacturer and a minor adjustment to the bias circuit solved the problem.

I just had two go out in a lot less time.

Thats a common thing in rogue amps. they are hard on tubes, factory Highly reccomendeds FACTORY matched sets only on outputs. those amps are great much better then most people might think. Ive spebt 2-3 times as much on 5 sets of mono blocks only to sell and buy new 120's.
hurricanes, vtl mb300, rogue zeus,ect

Tubes tend to die in two ways: (i) infant mortality, in which instance they die in the first 200-300 hours, or (ii) they live until the end of their normal lifespan. They rarely die in between.

You are experiencing infant mortality.

Amazing, thanks for the input. This is all valuable info for me.