Never used Peleton mode myself......not many of my fellow riders have the RTL515. It does sync all the lights around and needs to speak with them, so would explain the the flashing light in pair mode.I did find after posting (reading the manual!) that pressing the POWER button for ten or so seconds does reboot without losing any data.
Yes, I got the light blinking (somewhat drives a friend crazy but she's halfway there already!) but with no Edge, no radar. And now that I think about it, that may be part of what might have triggered this issue. I recalled "Peleton" mode and had briefly gone looking for it before that ride to reduce the blinking on following riders. But it looked like it needed pairing in Garmin connect or something and I did not want to jeopardize my Mission Control pairing so backed out. Maybe that upset things.