On both the emulator and FPGA hardware, only the start button works on real joysticks. This is because the joystick_tick routine assumes JOYSTICK_GET will set X to 0x01, which it only does for keyboard joystick emulation.

Real hardware (or emulator with SD card attached) only supports filenames with 8.3. So the release files can't be loaded.

Let's try this

Is it possible you could expand a bit on your thoughts behind the loadvram function?
As far as I am aware, you can not load data directly into VRAM with the LOAD function, but then were do you actually store the data?
The addresses are shifted right 4 times before you call loadvram which means that VRAM_TILEMAP becomes $0400. If you load the tilemap at that address, do you not overwrite your code at $080D and up ?

If I turn around corner very quckly, as early as possible, the artifact on that corner won't be picked up. So I literaly have to make sure that I bump into the wall before making a turn. I find it odd. Is it intended behavior?

I was on level 34 and had no keys at the time, when eventually, the skull in the corner started shooting fireballs in a pattern that made it impossible to proceed.
https://youtu.be/ray5JHGSrmA

Great job so far!

Had previously played the 0.1b version with the r34 emulator. Just built the r35 emulator with sound support and tried the 0.2b version. I noticed that the background music is sluggish, compared to the YouTube video. Unclear if this is some sort of issue with the emulator or my system (running Fedora 30, ALSA/PulseAudio).

Also noticed that if you die for the last time and the game is over, the sound is stuck on the last note until you elect to "Continue" or otherwise kill the emulator.

Loading the game from an SD card requires much more time to load all the files. This means that the start screen wouldn't show up on real hardware for a significant amount of time, during which the screen is just black.

Needed for the next release is an SD card image for testing. Also needed is feedback indicating load progress. This can be accomplished by simply printing to the screen which file is being loaded.

When scrolling between levels, there is sometimes screen tearing toward the top of the screen.

On a real YM2151 you need to wait a minimum interval between writes. You can check if the chip is ready by reading bit 7 of either address, it will be high when busy, low when ready (the emulator always returns low, so no worries there). Chase Vault has less/glitchy sound on FPGA hardware (it gets better over time played, but never perfect).

After clearing zone I returned to previous cleared zone, than back, and suddenly found myself trapped in the wall.
Now when I press cursor keys sprite animation works, but sprite does not move.