NTFS is not required for games bigger than 4GB, unless you prefer keeping full 1:1 ISO instead of wbfs split file format.
FAT32 is the recommended format, as it works with all other homebrew (Wii games ISO, gamecube ISO, emulators, media players, apps, etc.)
WBFS is still working, as long as you don't use "WBFS manager" which corrupts games. but it's never a recommended format, it works, but that's a deprecated format.
You didn't tell if you are trying games from the same region or another region. If it's another region, it might be a video mode issue.
You told you are using slot249, that's "obvious" I should tell. ALL the loaders are using that slot.
what is important is what's installed INSIDE that slot.
it could be outdated, or wrong.
if you want to know what's inside your slots, you can follow the syscheck guide in my signature and post the result here.
if you don't want to know, you can update or change it, it will overwrite the previous one without problem.
but I'm curious to see if the issue is because of outdated or wrong IOS version, so please post a syscheck log first.
when installing Sonic and the Black Knight it just black screens
You said "when installing" ?
is the problem when installing or when launching ?