The "filesystem not ready" means that there is a problem with the microSD integrity or that it's still reading from the microSD, maybe after switching slots rapidly. Try deleting the BUFF file from the microSD.
About the LOADING DDR, it's normal that it loads the DDR after exiting the menu or the first time that you power the cartridge. A part of the game is loaded into Flashes and another part loaded into RAM, once the RAM part is loaded and unless you do a reset, or change the game, the data will still be there and booting will be immediate.
So if you wait, let's say 30 seconds and then switch slot, up to slot 4, which is where the multi seems to be, does it not change to that slot 4?
From what I can see the games seem to work well, right? Can you try in a different slot.