Until you get your amp checked out by a reputable technician, all these comments are guesses at best. Blaming the JJ tubes might be correct, or not. As many have noted, poor shipping, handling, and such can damage any tube, even NOS.
JJ tubes are treated roughly in guitar amps and don't fail very quickly. I have used them in a Schiit headphone amp to good effect (6922). Sure, NOS might sound better, but if we want this hobby to continue with vacuum tubes or "valves" as they are called in Europe, then we have to be looking at new production tubes because the supply of vintage tubes will run out one day. What do you do then, move to Class D with Hypex or PuriFi chips?
Perhaps replace the JJ tubes with something else and see if they too get fried. If not, then you'll sort of know it might have been "something unquantifiable" with the JJ. But if they too get fried early on, then you definitely should get the amp looked at. Nothing made by humans is 100% perfect or as intended 100% of the time. Just the reality of manufactured goods.
JJ preamp tubes - repeated problems
I purchased an amplifier that came with stock tubes made by JJ. There were problems with the amplifier so I replaced some tubes and then figured out it was the pre-amplifier tubes and small tubes. The manufacturer in this case who is McIntosh did send me replacement tubes and they worked for a month or so and then began to crackle. Now I have to figure out which of the six small tubes is creating a problem.
I'm curious to know if manufacturers test the tubes that they use in the amplifiers before they ship them out? Maybe they test fine and then go bad within a month. I'm very suspicious they don't bother testing their tubes.
Judging by the process to test individual tubes and when you have 24 tubes on an amplifier I can understand them not giving them much attention during the manufacturing process. Maybe they expect people to replace all the tubes just like the power cords they send out.
.Many replace the stock tubes immediately with gold lions which seems like an easy choice. Maybe manufactures do test their tubes and they're just using a poor manufacturer.
Do others have tube problems with McIntosh amplifiers?