I had the same issue but thought it was just me. My solution was to rename the .rpx files, for example U-King.rpx to their actual name (The Legend of Zelda Breath of the Wild.rpx). I then imported that one single file. I don't have a lot of Wii U games so it isn't too tedious. Another way I found to avoid the Wii U freeze when scanning is to scan each platform individually. Hope it helps!
LaunchBox hangs when using Scan for added roms in WiiU
in Troubleshooting
Posted
I had the same issue but thought it was just me. My solution was to rename the .rpx files, for example U-King.rpx to their actual name (The Legend of Zelda Breath of the Wild.rpx). I then imported that one single file. I don't have a lot of Wii U games so it isn't too tedious. Another way I found to avoid the Wii U freeze when scanning is to scan each platform individually. Hope it helps!