sadly my varia 515 is a dud the light keeps switching off randomly either oaierd to my edge 830 or not..... very dangerous very unacceptable deeply disappointed... downloaded latest firmware etc still crap
I have the same problem, please see my thread here https://forums.garmin.com/sports-fitness/cycling/f/edge-830/244065/varia-radar---constantly-switches-off-on-and-changing-light-modes
There's probably nothing wrong with your 515, the problem is the firmware of the 830.
You could try contacting Garmin Support, but I've been waiting for about 6 months for a fix. They keep saying they're working on it.
Once Lockdown is over, I'm going to take my Garmin equipment to the nearest Zoo and see if the Chimpanzees can fix the issue.