Actually, I think it's the USB backup that I have mounted:

[root@fedora ~]# df -h /backup
Filesystem                   Size  Used Avail Use% Mounted on
/dev/mapper/external_backup  2.3T  691G  1.5T  32% /backup

It may also have been trying to work on the FUSE mounted directories, I'm not sure. In any case, this is a very unwelcome surprise for anyone with a large filesystem.

restorecon has been running for over an hour with this update (perhaps because I had some large filesystems mounted via sshfs?)

Same SELinux alerts as clnetbox. No additional information to add.