vidvnder Thanks, that's a great suggestion for a workaround.
In the AMD Adrenalin software, I enabled Radeon Chill (Gaming -> Games -> skate. -> Graphics) and set the idle and peak FPS to 75 (somewhat arbitrarily and pessimistically).
The setting has no effect on the initial startup screen, but after loading into the world, the FPS is locked to that number.
From that point, while monitoring RAM usage while playing, I witnessed at least three successful garbage collection events, and even though it looked each time like it was about to run out of memory, no actual crashes occurred.
It still gets pretty close to 100% RAM usage so I'm skeptical about whether this will prevent crashes completely (maybe I just got lucky), but it may at least reduce them.
Worth a try, but I hope there's a more robust EA can roll out for the game itself.