Hi guys, I've been lurking here for several months and have learned a lot from your discussions! Hoping you can shed some light on this issue with my Phantom 3 Professional. Yesterday I updated my firmware on my phantom and transmitter to the latest version, no apparent issues with the installation process. I recalibrated the IMU, did my compass calibration and my normal preflight checks before takeoff. I climbed to about 2 metres and released the stick to put it into a hover, but the phantom continued to climb at a very slow rate with 0.0 m/s indication on the vertical speed indicator. I descended the phantom back down to 2 metres and released the stick and it continued to slowly drop, again, no vertical speed indication. The altitude reading doesn't seem to adjust to these minor shifts in height , resulting in discrepancies; for instance it might read positive 4.5 metres or negative 2.3 when the drone is actually hovering at 1.5. The altitude and vertical speed readings DO seem to indicate intentional altitude changes resulting from control inputs, but not the changes resulting from the drifting. The issue also seems to be intermittent; sometimes the Phantom halts it's vertical movement immediately when the controls are released like it normally should, other times it drifts. I have made sure the phantom is in GPS positioning mode and not ATTI, and have recalibrated the IMU a couple of times, once after cooling the Phantom in the fridge. Any ideas what might be causing this? The firmware update? IMU issue? Something wrong with the barometric sensor? Any suggestions on how to resolve it? Many thanks for your assistance. Best wishes.