As with the update to 3.5.1 in the preview Channel, updating to 3.5.5 stable made this bug came back. GPU is oscillating between 200 and 1040 MHz, creating stutters and framedrops in game. Setting GPU to manual mitigate the issue, but this Is very annoying for a stable update. Just making a post to gather all of us and maybe get some attention from Valve.
Got the 400/200mhz bug on my old deck too, solved It with an RMA. This one seems to work differently, it was not present on 3.4.11, got it on 3.5.1 preview and disappeared with a downgrade. Also setting the GPU clocks to manual solves the issue, and the deck doesnt throttle as with the 400/200 MHz Bug. I will contact Valve this weekend to see what they have to say about it.