Hi! After some digging, I have found the kernel option/mmodule that causes this: HID_LOGITECH_HIDPP. I presume my mouse (Logitech 903) is handled by this module (hid_logitech_hidpp.ko), though it's not strictly needed.
Things that work to make the original problem go away: - Build a kernel with CONFIG_HID_LOGITECH_HIDPP=n - Blacklisting the module (add `modprobe.blacklist=hid_logitech_hidpp` to GRUB_CMDLINE_LINUX in /etc/default/grub Things that _do not_ work: - `rmmod hid_logitech_hidpp` (no error reporting it's in use, I presume libinput just makes a decision on whether it's there when starting and never reverts, even if the module goes away). My best guess is that not all of userspace is ready yet for this hi-res stuff --- not that I found anything that worked really well with it (tried: Vivaldi, a Chromium-based browser, assorted Qt and GTK apps). Since there is an acceptable way out for me, this bug could be closed. OTOH, this is very hard to debug breakage, so just relying on people finding this bug is maybe a bit harsh. Your call. Best, Tobias