Actually even i had this problem. Yesterday i joined windows insider dev program. after joining i couldn't find the copilot. so the next day morning when i opened my laptop, i found copilot. But when i tried to open, it is not opening. I tried several times, but it is not opening.
I've had this problem and this is what I discovered.
I use Canary Edge as my browser, if I open Copilot it doesn't work.
If I switch to Dev Edge Copilot works, if I then switch back to
Canary Edge Copilot works until I shutdown for the night.
I then have to do the same process this next morning.