OK.
Things you could try;
Start in safe mode and try option 5.
Try the other USB port.
If the USB is plugged in when you power on, try removing it and plug in once the PS4 has booted. If it's the other way around, try that the other way around.
If you have another use stick use your pc to copy the saves you want and try that. Remember to keep the same file structure.
It could be there is some file corruption on the USB stick. Fingers crossed something up there works