We’ve built a WebGL game with Unity and it runs fine everywhere except on iOS browsers.
For simplicity of understanding and referencing, I’ll write down noteworthy points in number-point format:

1. Game has 2 scenes. One is UI-only and the other full of 3D and vfx. Game reloads during the 2nd scene at a random time.
2. We pre-allocate all memory we’ll need. That’s 1GB. We’ve observed that the game does not reach that limit during that loading event. Not on any platform including iOS.
3. Prior to adding a lot of new VFX, the issue would not happen.