I sometimes see blue plus signs popping up in the headset

This is a result of your headset or controllers being on the edge of the guardian that you set up. To solve this you will need to reset the guardian to be a larger area.

To reset your Guardian in VR (Oculus guardian setup video):

1. Select Settings from the bottom toolbar.
2. Select Guardian in the left menu.
3. Click Set Up Guardian.
4. Follow the on-screen instructions to reset your Guardian.