I get this sometimes with the Index… I have to unplug it and back in by disconnecting the power… And than doing the VR start again… Most the time it works… But sometimes it ask you to center again, and you have to center it first (on flatscreen since all you can see) than restart the VR.
The other thing I found is DON’T LET the vive shut down your Light Houses… Keep them on all the time while Restarting and starting VR in FS2020… If you don’t this problem happens like 75% of the time. In other words before starting FS2020… Make sure your light houses are already ON! Than shut off SteamVR… And than in Game use the hot key to start VR again… Your light houses already on, the HDM should go on pretty quick… (most the time)