Runner registration is forbidden

Up until an hour before my demo, everything was fine. Runners were working as expected.
I had CE 10.7.1 (now 10.7.2) installed, and the runner installed via Docker.

I’m not sure what happened, but Docker was no longer responding, and I was forced to shut down my runner server. In any case, I attempted to bring it back using the same steps that I did before, only to encounter this problem:

ERROR: Registering runner… forbidden (check registration token) runner=YTYgyPP9
PANIC: Failed to register this runner. Perhaps you are having network problems

Since then I have upgraded to latest version, and installed the Linux runner as well as the Docker runner, and both fail like that. I assure you that the token is set up properly.

Linux runner is using 10.7.1, and Docker runner is :latest.