The U-Boot stuff is just U-Boot USB support being half broken, which is a known problem. Your machine/hardware is fine. I already fixed over a dozen bugs in that stack, but it looks like we need to fix more. Sure would be nice if someone volunteered to spend some time on it… 
If it spams and boots fine, you don’t need to worry. If it locks up that’s less than ideal, but you can just work around it by unplugging your USB devices and plugging them back in after boot (or at least after U-Boot initializes). Sorry that this still kind of sucks…