I have that same problem and as far as I can tell, it’s a hardware failure.
Have you had any high temps (~100c) or overheating related issues? I’m not sure if it’s just coincidence that my keyboard failed after I started getting those or not.
Regarding the 0.55Ghz issue, I have spent a lot of time doing various tests in coordination with Framework Support lately, and at least in the case of my device the issue seems to be due to over heating. I can reproduce the 0.55ghz fault by running 3D Mark’s Steel Nomad stress test (windowed) + Cinebench R23 multicore test, and about 10 minutes later the cpu will throttle to 0.55Ghz. I’m still investigating a solution as my board is now out of warranty, but my GPU plugs seem to help.
My overheating issues were due to the vents needing to be cleaned. I’ve also ordered a new keyboard.