If anybody knows how to get in touch with Manuel or Vincent van Dam, please let them know.
I have a Sony HB-F1XD (MSX2, not the -J 2+ model) and have been running everything from a MFR SCC+ SD w/ 512kb expander and FM-PAC for music.
I noticed quite a few issues loading dsk files using opfxsd, so I've been using SofaRun as my primary loader. This was working fine until I started developing my own music for my own game, using MoonBlaster, and also attempted to play a) Awakening and b) every game by Kai Magazine -- none of them loaded and with bizarre errors.
By pure coincidence, the only version of MoonBlaster that works on my unit using MFR on a .dsk is the 1.4 BASIC version available from this website. The newer updated version from MSX-Banzai does not work at all, unless I keep the files in a folder (without a dsk image), disable the mapping using MAP.COM from A:\BIN\, and then run them after returning to BASIC.
I'm told the dsk emulation by MFR is based on DSK2ROM. All of Kai's games use DSK2ROM, which is obviously why they are having the same issue - there has to be a conflict somewhere.
If any of you have had trouble running homebrew games using the MFR, or loading .dsk images period, then it's more than likely due to this glitch. The only way to bypass it afaik is by using the steps above - extract the files to a folder on the SD card, run MAP.COM, and then exit to basic and load the files normally without the mapper.
(huge thanks to Discode @ the MSX development discord for working with me to identify this issue.)

it's in the root of the MFR folder normally.