@Robotron I think it’s just bad luck, I doubt you’ll have issues going forward, if there was a design issue w the amp it would be common knowledge by now. I hope things go smoothly after you get the amp back, the sound is worth it.
Regarding power tubes, as others have said, no need to match if you have some form of bias adjustment. I actually just went back to the stock KT88s that came w my Willsenton R8 to preserve the life of my Golden Lions now that they are so much more expensive, and I can’t really say I notice a difference. And one of my original tubes is different because it was a replacement they sent me after one of them arrived with noise issues, so I know for sure I don’t have a matched set. In fact the internals look slightly different then the other KT88s. Lol it’s stamped KT88 but for all I know it could be a 6550. Sounds great though and it’s been about two weeks since the swap.