Comment # 2 on bug 955079 from Johannes Meixner

The issue is not caused by openSUSE patches for sane-backends
(because there are no such patches for sane-backends).

When the root cause is in sane-backends then it is
a SANE upstrem issue which you already reported in your
"regression in sane-backends 1.0.25, AGFA Snapscan 1212U_2 not found"
mail thread at sane-devel@lists.alioth.debian.org

But the root cause could also be in the kernel or in libusb.

When your scanner is connected at a USB port where
the kernel module xhci_hcd is used (see "lsusb -t")
then it is likey a duplicate of bug#856794.

Details:

In general "sometimes works / sometimes fails" indicates that the
root cause is somehow hardware related where "hardware" means
the actual computer hardware plus the computer's built-in
firmware (i.e. BIOS or UEFI) and "hardware related" means
computer hardware plus firmware plus Linux kernel driver
plus low-level hardware related software (e.g. libusb).

There are currently issues with scanners at USB ports
when the kernel module "xhci" is used as kernel driver.

When "lsusb -t" shows "Driver=xhci_hcd" for the USB bus and port
where the USB scanner is connected (see "lsusb" where the scanner
is connected), then there could be issues depending on the
computer hardware and firmware.

In this case see
https://bugzilla.opensuse.org/show_bug.cgi?id=856794
in particular see
https://bugzilla.opensuse.org/show_bug.cgi?id=856794#c24
that reads (excerpt):
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My machine has 4 USB ports, two labeled with
the "super speed" USB logo (a.k.a. USB 3) and
two labeled with the normal USB logo (a.k.a. USB 2)
but for all 4 ports xhci is used and it fails on all 4 ports.
-----------------------------------------------------------------
and see
https://bugzilla.opensuse.org/show_bug.cgi?id=856794#c40
that reads (excerpt):
-----------------------------------------------------------------
It depends on the computer hardware where "hardware"
includes the computer's firmware (BIOS or UEFI).
There are computers where USB3 always "just works".
There are computers where USB3 fails under certain conditions.
Perhaps there are computers where USB3 always fails.
-----------------------------------------------------------------

When your scanner is not connected at a USB port where the
kernel module xhci_hcd is used as kernel driver (e.g. when
your scanner is connected at a USB port where the kernel
module uhci_hcd or ehci_hcd is used as kernel driver),
then have a look at "Trouble-Shooting (Debugging)" in
https://en.opensuse.org/SDB:Configuring_Scanners

For example to get USB debugging information
you could use comands (as root) like
-----------------------------------------------------------------
export SANE_DEBUG_SANEI_USB=128
scanimage -L
unset SANE_DEBUG_SANEI_USB
-----------------------------------------------------------------