Without make, model, and a long story I can't guess what's going on here. Since you can access this stick the MOST IMPORTANT THING TO DO RIGHT NOW is to back it up so in case this stick is getting wonky you won't lose anything.
This get a new stick and retest.
i have been messing with it a lot, using it to install windows, store data, etc.
suddenly there is ONE 3.0 port on my laptop, which works perfectly with all other USB devices (2 and 3), but this port will NOT see the flash stick any more! strange, because it sees everything else, and the other USB 3.0 ports DO see the stick! also another laptop DOES see the stick!
i have to conclude there is a particular problem between this particular stick and this particular port. but what is it??