This one needs a new hardware test.
The game is writing to $420c (HDMA enable) at V=142, H=~1108-1110.
This is the starting point where HDMA starts running when enabled.
So it ends up being a race condition. When H<=1108, it causes HDMA to run on that scanline, which throws off the HDMA line table by one. That causes the screen to shake as it constantly hits and misses that point.
We must make an SNES test ROM that identifies exactly at which point the values written to $420c are latched. It is definitely H=1106 or earlier, and not H=1108 as I do now.
https://archive.is/LxuUv
Near:
test roms: https://github.com/undisbeliever/snes-test-roms
Fixed: https://github.com/byuu/bsnes/commit/07427e4697f947542e9e57c0af6bf8f91935d654