Altimeter freezes after sleep mode

Hi, I'm new to Explore 2. I have noticed that during activity if I put device to sleep mode and than wake it up and resume activity - the altimeter stops working. All other parameters are fine, but no ascent gain, no current gradient etc. 

Am I the only one or is it kind of Explore 2 known bug?

My FW is 20.18, so the newest one.