This is how the old DML was, the one that kept Nintendo's original codes, it worked fine for most games but the no disc compatibility was very low and games would crash a lot, also it was slow!
Well, This new one has problem of Actually working - only whenever it wants.
I tested with Dios Mios Lite 2.6 and I can... "happily" I guess to inform it does not seem to have any problems, but with Dios Mios 2.6 installed I still am having problems, after I have downloaded the WAD three separate times and tried to install it from each at least three times around to test it just seems Dios Mios either does not Show up about 80% of time at all, and Boots the game - once when it feels like. It may be something with my Hard Drive that is not filly working with Dios Mios, as my hard drive would fail to boot a game with dios mios - maybe 10% of the time, but generally works. As for actual game loading from USB with Dios Mios 2.6 installations I done, yeah, seems to work, even down to multidisc I tried with my Killer7 Backup.
But Yeah, if you ask me "Would you want to keep a disc in a drive to boot gamecube games from USB, or would you like to play your disc games once in month" I would go with the first one gladly.
I am still testing but indeed, Dios Mios Lite 2.6 did not have disc load problems with 5 out of 5 attempts. Too bad I do not own any large enough SD card media, plus I like to use just 2GB SD card with my Wii for compatibility with games that do not support SDHC and for the fact I have already large enough USB drive that should fill every need a hole can have.
EDIT: I think I know the problem for most parts: It seems Dios Mios, even when booting disc, needs to initialize the USB drive. This is problem because my USB hard drive is not always initialized right to work with Dios Mios. I may need to crash the wii once or twice before Dios Mios works right. Normally with third attempt I can get gamecube games always boot until I need to disconnect my USB hard drive for reason or another.
But even this is false because Most of my attempts still end up in black screen hang after getting a game booted from USB few times. If possible, Dios Mios should revert to old way or find a way to not try use USB media, I can see the Hard Drive being accessed when trying to boot a game even if it ends up in crashing.
So, I cannot say for sure at all, but I know it is probably media access error even though It should be just booting a Disc