you only press the rekordbox button when you’re connected to a computer or iPhone/ipad to use the rekordbox library on that device.
if you’re using a USB stick, just press that USB button like you have been doing…
your USB sticks are fine, they are working as normal. i don’t understand why you think something is wrong.
as i said, the rekordbox button accesses a rekordbox library on a laptop/ios device. so if you plug your iPhone into the usb port of the CDJ, you press the rekordbox button to be able to ‘see’ the rekordbox music library on your phone.
those buttons simply tell the CDJ what media you want to read from. to be clear, the rekordbox button is not needed unless you’re intending to play directly from your iPhone or a laptop.