SteamVR,Unity5.5.3 - WaitGetPoses drops causing performance spikes

Hello,

Attached is a trace of performance for our game.

We see WaitGetPoses drop to nothing for roughtly 3 secs and then pop back up.

This causes nearly everything else to pike up. Very bad.

We see this every 10 secs of so. It seems to be independent of any section of the game. Vsync is turned off and RenderScale = 1. Unity 5.5.3.

Any ideas what could do this?

Thanks