How to trace/fix mouse speed changes that aren’t reported by xinput?

Occasionally, for an unknown reason, my mouse suddenly starts moving faster, I think it’s acceleration but it might be speed. It happens using desktop apps, and in the middle of CSGO fullscreen sessions; it’s occasional and unpredictable and has been happening all the time I’ve been on Bionic AFAIR.

I’m on “KDE Frameworks 5.47.0”, plasma-desktop 4:5.10, using Kubuntu 18.04.2 (bionic). The mouse is a Logitech M185 wireless.

I use something like this:

xinput --list-props 11 | tee xinput_mouse-11_20190731d2.out 

to get the xinput properties for comparison (then meld ./xinput*.out for diffing). However they don’t change when the mouse goes fast!

If I use the “Mouse – System Settings Module” (/usr/bin/kcmshell5 mouse) I can alter any mouse setting (eg left -> right hand), apply and get back to my desired mouse settings, ie the cursor moves at the required speed again.

So it seems that xinput, and kcmshell5 mouse both still have my desired speed/accel set. The weird thing is that none of the properties are reported as changed in xinput when the mouse clearly is not working the same.

Now, in investigating I’ve found xset m, this appears to do the mystery setting, the properties shown in xinput don’t alter and the speed/accel goes to about what I think I’m getting with the transient error … xset only sets AFAICT, it won’t display and the man page doesn’t say where it is writing settings too. It sounds from passages like:

Threshold is just an integer. The setting is applied to all connected pointing devices. xinput(1) should be used if you need device-specific settings.

That it saves settings to the same place as xinput, but then why doesn’t xinput report the changes?

To repeat: if I do xinput --watch-props 11, then run xset m nothing is reported by watch-props but the mouse speed increases. However, if I then open up kcmshell5 mouse and toggle the “reverse scroll” property then only the following is reported:

Property ‘Evdev Scrolling Distance’ changed.
Evdev Scrolling Distance (285): -1, -1, -1
Property ‘Evdev Scrolling Distance’ changed.
Evdev Scrolling Distance (285): 1, 1, 1

but we’re back at the desired properties.

So, any insight, how I can trace the bug that’s happening (what system it’s in) how I can tell quantitively the accel/speed the system is currently using (as xinput is clearly not showing it); and if possible how I can fix it so mouse settings don’t alter themselves randomly.