I think @thelmuth is likely on it. I have a post that tells a bit about this here.
If you’re having the same issue at higher power then it’s likely a tube failing. I’ve heard of people with this new, from a vendor. I also hear people tell me they’ve gotten 8 years or more.. I don’t think you can predict failure of these it seems like a crap shoot.
I’m on tube three, I figured I get about 2 years on each of mine. It is hot in the desert SW and can reach 115F… I think this accelerates failure.
I have to point out that even good tubes at low power settings have a TEM01 or doughnut shape. Many vendors want you to run it at higher power, likely 30%, it should work.
You can lower the pulse time from the console, from continuous to so many milliseconds. Lower it until you get a legible burn mark. But if it’s not cutting well, it’s likely the tube going south.
I had one that went from fine to bad over a three day weekend.
Good luck, let us know…
