Can't play newly transferred videos in usb after inserting to another device

so here is how it goes:
I have a 500GB SanDisk USB, when I transfer videos in it, the videos work.
after transferring the videos to our Affordabox (basically, like a cable box or DVD box) the videos in the USB still work.
I reinsert the USB to my computer, test the videos in it, and they still work.
BUT when I transfer new videos in my USB after the above mentioned have already been done, the new videos won't work, they will continue to load indefinitely and when I try to play the newly transferred videos in our Affordabox, it would say that it is an unsupported file.
pls help
P.S
the usb gets repaired if I format it but will have the same issue again if I do the above mentioned