Adjusting the 'Pointer speed' mouse setting in Unity has no effect

- What is expected to happen:
  Pointer speed (mouse sensitivity) adjusts according to the slider's position.
- What happens instead:
  The setting has no effect on mouse, though the slider can be moved freely.
- How it happens:
  1) Log in into a Unity session;
  2) Go to System Settings > Mouse & Touchpad > Try moving the slider to either side;
  3) The new values are not applied, pointer speed is not updated.

Whenever the slider's position is moved, the "speed" key in "org.gnome.desktop.peripherals.mouse" gsettings schema updates accordingly, however the "libinput Accel Speed (290)" property does not. It stays at 0. Manually setting a value to this property (xinput --set-prop device property value) has an immediate effect.

This setting works as expected during a GNOME session. Both the "speed" key and the "Accel Speed" property update as the slider is adjusted.

Ubuntu 18.04.5 LTS;
unity 7.5.0 (=7.5.0+18.04.20190304-0ubuntu1);
lightdm 1.26.0 (=1.26.0-0ubuntu1).

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: unity-control-center 15.04.0+18.04.20180216-0ubuntu1
ProcVersionSignature: Ubuntu 4.15.0-112.113-generic 4.15.18
Uname: Linux 4.15.0-112-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.17
Architecture: amd64
CurrentDesktop: Unity:Unity7:ubuntu
Date: Fri Aug 28 18:34:50 2020
InstallationDate: Installed on 2016-11-03 (1393 days ago)
InstallationMedia: Ubuntu 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
SourcePackage: unity-control-center
UpgradeStatus: Upgraded to bionic on 2020-08-17 (11 days ago)