I have been having this problem for almost a year now and still haven't found a fix, it usually crashes about an hour into a game or something like that. It either freezes, or bsod.
If somebody could help me fix this issue I would really appreciate it.
Going to need more info.
Please state your PC specs, specific Vega 56 model and if it's overclocked or running default settings.
Also, when you get a BSOD, which error message does it give
I had a problem similar to yours before. My computer was restarting itself especially while playing heavy games. There wasn't any problem while playing League of Legends. Sometimes it may restart randomly on idle. When I take look on Event Viewer, I saw the problem named "Kernel Power 41 (63)"
I tried to fix it for 6 months. I changed my PSU but the problem caused by rams. Even after it passed memtest for long hours. I sent my rams for rma and got new ones. Not a single problem happening now. I hope this helps.
Oh by the way, it was not just restarting problem. As you said, it was giving bsods, freezing, all kind of boring stuff.