I use simple-scan on Manjaro KDE with an HP Envy 5542 aio printer / scanner.
After sane was upgraded to 1.2.1, simple-scan fails with the error message “Failed to scan - document feeder empty”. There is no document feeder on my scanner. Downgrading sane to v. 1.1.1, everything works as expected.
I reported an issue at sane is looking for non-existant document feeder (#654) · Issues · sane-project / backends · GitLab
This post is in case other Manjaro users have encountered the problem, too.