Weird USB port behavior

#1 flash drives are not for backup. I strongly recommend backing up important files to a medium that is not prone to getting lost/destroyed or failure

#2 electronics do not always fail abruptly, there can be many levels and modes of failure that may not be total or repeatable and they can manifest as strange behavior as you are seeing here. Your usb drive or port may be failing in a way that puts it right at the edge of a specification such that some drives/ports are able to overcome and some are not. Or it might be a problem with the physical interface if you use the same drive in the same port a lot. Imagine if pin 1 on both the drive and the port have worn out in a way that the connection isn't solid. A less worn pin 1 on either side of the connection would be more reliable than these two particular devices together. Maybe try cleaning the contacts. Or it might be a stupid driver problem.