It can be two different issues, or the same.
USBLoaderGX read the animated banner from the game file, and extract it to keep a copy on SD or USB for faster loading of the loader's interface.
If the banner was badly extracted, a "bad copy" is stored on your SD or USB and will always be used and displayed as black screen, instead of retrying to read the banner from the disc.
solution : delete the banner manually from cache_bnr folder, the one with your game's TitleID.bnr
when the banner is bad, it doesn't necessarily mean your game is bad, but most of the time it is.
so, if the problem was the extraction step, and the loader did a bad work, you get a black banner, but the game should work. in that case, it's only a loader's issue because your game works.
If you have a black banner and your game doesn't work, the issue is not the banner extraction from the loader, but really that your game is bad, unreadable, corrupted, etc.
So, you said WBM could check md5/Sha1, and reported it as good ?
this is strange.
is it an official game, or a modded one ? (added, custom levels, etc.)
Did you check the ISO on your PC, or the WBFS on your FAT32 Wii HDD ? be sure to verify the one the loader will use.
PS:
a RIP (or a dump) is the action to make a copy of a physical device to binary file.
Wii Disc -> Wbfs file
a bad rip, or bad dump, or corrupted dump, is a bad copy.
Personally, I prefer using the word "dump" as I always used "rip" for another meaning. a rip for me would be a modified ISO with deleted content to make it smaller (replaced video with dummy, etc.). ripping being action of removing, cutting, tearing. while dump is a full clean copy.
I think it's just me who think like that, as rip is action of extracting from the original source : TVRip, CDRip, DVDRip, etc.