Reformatting my flash drive FAT32 definitely fixed my issue. My new Android originally recognize this flash drive and I transferred a lot of files using it while attached with the small adapter piece (not a dongle). But it stopped recognizing the flash drive yesterday, and I can't see anything that I did that would have changed it. I definitely had not reformatted my flash drive to make it stop working. But formatting it FAT32 made the Android instantly recognize it again, and I was able to start transferring files to it again.