canon630u backend stopped working some time prior to 2008 and hasn't worked since
Attempting to perform a scan or preview with any scanner supported by canon630u backend fails and causes the scanner to stop responding to any requests until it is reset (with usbreset command or by unplugging and plugging it in again).
This bug has been reported repeatedly in distribution channels by different users but as far as I can tell it has never been reported here.
Here is a log showing the result of running usbreset followed by SANE_DEBUG_CANON630U=123 scanimage > /dev/null twice:
Here is a selection of reports of this bug in other places, dating from 2008 to 2020:
- https://bugs.launchpad.net/ubuntu/+source/xsane/+bug/289446
- https://bugs.launchpad.net/ubuntu/+source/simple-scan/+bug/1315702
- https://bugs.launchpad.net/ubuntu/+source/sane-frontends/+bug/118843
- https://bugs.gentoo.org/34024
- https://www.mail-archive.com/debian-bugs-dist@lists.debian.org/msg1746768.html
Perhaps a clue, "scanner works on OHCI, but not UHCI":