Custom build
GPU: AMD Radeon RX 5700 XT Red Dragon 8GB. No overclocking.
CPU: AMD Ryzen 5 3600. No overclocking.
Heat Sink: CRYORIG H7.
Mobo: B450 Tomahawk Max.
RAM: Corsair Vengeance LPX 16GB (2 x 8GB) 3200MHz. No overclocking.
PSU: Corsair TXM Gold 550W.
Case: NZXT H510 (Replacing soon).
Fans: 2x intake: BeQuiet! 120MM Pure Wings 2, 2x exhaust: Noctua NF-P12 Redux.
Operating System: Windows 10 Home. Version 1903.
GPU Drivers: Adrenalin 2020 Edition 20.4.2.
Issue
I built this computer in June. Since then, it's pretty much had no issues, until yesterday. I had been playing a game (Divinity: Original Sin 2) without issues for around 20 hours over the two weeks prior to yesterday, but yesterday the game froze and crashed to desktop. I could still hear talk on Discord while it was frozen. It did the same thing 3 or 4 more times over the next 10 minutes. After being stable for a while after that, I started getting white flashing lines appearing at random on the textures in-game. The game soon crashed again. Today, I tried playing Forza Horizon 3, and it was absolutely fine for an hour, but then froze and crashed to desktop. I was trying to type a web address into Firefox and my computer locked up, went to a black screen for around a second and then came back and the text I was typing appeared. The computer has also locked up when loading AMD Ryzen Master and one other time when doing light computer work, both of which required me to force shutdown my computer.
Troubleshooting Attempted
As said, everything was fine up until yesterday, except for the very occasional tiny lock up. My instincts tell me it's either a GPU or PSU issue, but I'd like some further help.
Thank you for any help.