Rift S tracking can be randomly flakey. If this happens again and again, then worry about it, but don't lose too much sleep over just a single incident.
Agreed.
Additionally, at the time the headset poweres up,, and the time that it's initialised, try to ensure that as few of the tracking cameras as possible are obscured, and the headset is alighed in the same direction your head will be and with roughly the same view that you will have.
The rift S could really do with an option to reset the headset tracking whilst it's running. For example, once it gets the idea that its grid is at at an angle, say 30deg left of straight ahead, that's it., possibly for days, even weeks..... :/ anyhow, I'll live with it for the time being and move to a different brand of headset when the rift needs replacing, or Facebook's nagging to migrate authentication becomes too onerous...
@Craith - I think by guardian, the OP is referring to the play area boundary that you set up when configuring the Rift S (or when the Rift loses track of it surroundings). If you get too close to the boundary, it becomes visible as a grid. This should prevent you bumping into things when playing standing up in VR. If you are only playing seated games, you can tell the Rift S not to fully calibrate the Guardian boundary. Then, you only need to set the ground level by lowering a controller to the fllor when prompted.