Beginning Jan 26 10:47:02 I've been getting thousands of
/dev/sdb is a USB-attached external drive, when I attach one, which is
for a few minutes at a time. The errors happen all the time. (The block number changes.)

This uses /dev/sdb so that an attached drive is assigned
/dev/sdc instead.

Is this a problem with my USB hardware?

If there was something wrong with the usb hardware then anything plunged in that port would show errors (assuming you have other flash/ssd devices).
Fat 16 and Fat 32 is most likely the problems since they are prone to generate file system errors (not bad block errors). follow the the link to do the repair. Make a backup copy (use dd or any cloning method as backup). File system backup tools may not be able to read the contents of the drive. One more thing trying to mount this drive and writing to it will only make thing worse.

https://askubuntu.com/questions/1472...32-file-system

There is no file system; there is no drive; the word 'phantom' in the title indicated this.