My guesses are that there are a lot of 3D stuff going on in the games and some instructions probably isn't covered in the jit yet(that's why MH3U is very slow right now I think).
For MH4U it would help to have a rom hack to force the 3D effect off, I tried looking into it once but I don't have any leads when I disassembled with IDA Pro. In MH3U/MHGen you can see a difference when you set the 3D to On or Off in the main menu even on Citra, the upscaling kinda breaks if it's set to On but looks fine when it's set to Off.
Maybe someone more knowledged than me could find the subroutine that controls the 3D effect in 4U. I already tried running Parental Controls to launch it in 2D on my 3DS but it's the same, I also did it in 3U/Gen and there was still a difference when you set the 3D to On/Off in the main menu in-game despite being run in 2D. DQ8 can't be run in 3D at all so there has to be a way for MH4U to behave in the same way through rom hacking.
But yeah it's great to see all sorts of activity with the project