I think those are symptoms of the NAND being overfull. When you import a NAND dump into Dolphin, Dolphin merges the contents of the imported NAND dump with the existing Dolphin NAND. So if you have, say, 200 MiB worth of WiiWare games installed in Dolphin and 400 MiB of various content in your NAND dump, you'll end up with a total of 600 MiB (assuming there's no overlap in content between the two), which is over the 512 MiB limit.
So, my suggestion would be to try deleting the contents of the Wii folder in Documents/Dolphin Emulator/ before importing the NAND. (This will delete all Wii save files and other Wii data, so I would suggest making a backup of the folder first.)
So, my suggestion would be to try deleting the contents of the Wii folder in Documents/Dolphin Emulator/ before importing the NAND. (This will delete all Wii save files and other Wii data, so I would suggest making a backup of the folder first.)