Mountain bike activity goes in standby

When i start mtb activity, after 10 minutes screen gon in standby, and i see whatcface.

I try in mtb options, i find time-out normale or long, but is thr same

I use fenix 5 plus with original  heart rate strap, and akmountain bike data page.

Other bug, after 9.0 software upgrade, is that when i start mtb activity, some time , SmartWatch, go to whatcface , and i must repeat 2 or 3 time , this operation to start monitor my activity