Help me diagnose the problem

I'll state the obvious, have you called Rogue back?

I agree with the comments above. My amp does not have separate fuses for each tube. So, if I blow tube because it arcs, there's a good chance I took a bias resister along for the ride too. And I agree that changing out a bias resister is an easy fix.

As an aside, I've had a brand new tube arc and blow a bias resister. But more often it's old power tubes that are more likely to arc.

ARC recommends that I change out power tubes every 2000 hours. Don't know what Rogue recommends, but you mention in the OP that your amp is 4 years old. Have you changed out your power tubes yet. If not, you may be way, way overdue.

Otherwise, the advice above is reasonable, including calling Rogue if you are not able to easily resolve the problem. FWIW, tube amps are pretty robust. The only repair issue I ever had with my amp was a blown bias resister -- and that can happen anytime.

In case this may help. I just resolved a somewhat similar problem today with one of my AirTight ATM3 monoblocks.

Earlier this week, the right amp popped, and I gradually lost volume. I shut down the amp and as the amp has built in bias meters, powered back up looking for any issues with the output tubes. All seemed ok, but I was getting no bias readings at all.

Tested the power and input tubes and discovered a 12ax7 tube was weak. I alsoI tested both fuses and noted one showed slightly open but still "good"

I replaced that fuse with a new one and am back up and running.

I hadn't called Rogue- I plan on doing so on Monday, but I already heard from Mark. On the Rogue each tube is individually fused and biased. So far after switching things around the fuse is still holding but I have been exceedingly careful to play music at very low levels. I feel the errant tube is shorting when pushed and thus blowing a fuse.

Supeisingly I have not had any success yet finding replacement fuses. Nothing at Radio Shack or at a local musical instrument store in stock of the correct value.

I get my fuses as well as tubes from Mark (Rogue). If you order tubes from him he may not even charge you for fuses and just toss a couple in as a kind gesture. Amazing customer service.