We understand that you're experiencing an issue with your Quest 2's Guardian frequently crashing, even after restarting it several times. Please make sure that the play area you're using has a good amount of light and enough open space for movement. Next, try setting the boundaries for your Guardian by either setting to Roomscale or Stationary. If you are playing to Roomscale, you will need to manually set the boundaries of your play area, and Stationary will automatically set up a small barrier around you.
If you are having an issue in both settings with your Guardian crashing, please try submitting a support ticket here, so we can get to the bottom of this issue and get it resolved for you.