NFS Heat Stutters After a While

I've had NFS Heat since last year and decided to pick it up again, recently. However, since yesterday, my game begins stuttering after a while. Either after 10-20 minutes of playing it or after just 5 or less. A problem I never had until now. What happens is that the game sits at around 30 FPS initially and can go up to 40 depending on what's going on (less lighting effects, less particle effects, no car crashes, etc.). And after a while, it dips from 30 to 14-20 FPS. Occasionally it'll go up to 29 FPS, but the stuttering never really goes away.
I've tried methods posted on Steam forum discussions and from guides to stop the stuttering but they're not working for me. I've tried capping the framerate on AMD Software between 30 FPS and 60 FPS and it doesn't work. So far the only solution I have is pausing the game at any point, going to Settings > Graphics and changing the game to windowed mode then going back to fullscreen. And even then, it stops working after some time. I've also tried quitting to the main menu and reload the game, which works but it keeps me from doing any events or even customizing cars without the game stuttering again like before. I've also checked the task manager to have a look at the game. And whenever this starts happening, the GPU usage is at 100%.

If it helps, here are some of my PC specs:

• MSI B350M Bazooka
• AMD Ryzen 5 1600 Six-Core Processor 3.20 GHz
• 24 GBs of RAM
• Radeon RX560 4GBs