If you read the recent blog posts on WKWebView, it can use more memory, especially for music tracks. Does your game use a lot of music? I'd suspect it is crashing due to running out of memory.
It does use a lot of music, though as it seems to crash when a new scene is loaded, or when the game is paused, I suspect it has to do with my system for saving save slot screenshots to json, which happens when you pause and when the game autosaves at the start of a new scene.
Any idea why the game is playing every sound effect simultaneously? This even happens when the window is changed/device is locked for a second, and then the game is returned to.