I have had this problem since the start, and now it really annoys me. In Steam VR, after launching certain games (revive especially, also vorpx), my position sinks down. I can redo the room setup but it will happen again half an hour later. Any ideas for a fix?
Hi Jonny, well noted with thanks. I will update this reply soon once our engineers get to work 
Due to lack of positional tracking, this happens a ton. SteamVR sometimes resets the height to nothing when recentering. Now, if the Piplay software allow for a recentering button (key bind and/or headset power button press) this might be fixed.
Hi Jonny, what’s the version of Piplay & Firmware you used at present?
1.1.92 and the latest fw.
After I used this app, I never had any problems:
http://www.kegetys.fi/floorfix-tool-for-re-calibrating-the-floor-level-in-steamvr/