@martinbailey74
The only gamepad driver I have installed is xpad. I picked option 1 - DisplayYesNo for the security mode. I did have some trouble on the initial connection, so you'll want to select the background option under the Configure bluetooth connect mode. Once you have that, try connecting the Stadia again. Whether it connects or not, select to remove a bluetooth device, pick your Stadia from the list, and then re-connect after that.

I'm not sure why this would work for any reason, but these are the steps I took and it works for me now, and pairs right up after a reboot when ES is done loading. One other thing to think about is if the Stadia is pairing to something else before the RetroPie grabs it.

What color light are you getting on the Stadia when you're having difficulty connecting after a reboot?

**Update: I recently had some trouble with connecting my Stadia, so I changed the connection mode to "default", which seems to have fixed it. You can try both modes and see if one or the other works for you.