I have exactly the same issue.
Touchapd Synaptics TM2869-008 working perfectly fine with kernel 4.15.0-70 under Ubuntu 18.04 LTS. As soon as I updated kernel to 4.15.0-72, touchpad stopped working.
Booting back to previous kernel, touchpad is working perfectly fine.
I have exactly the same issue.
Touchapd Synaptics TM2869-008 working perfectly fine with kernel 4.15.0-70 under Ubuntu 18.04 LTS.
As soon as I updated kernel to 4.15.0-72, touchpad stopped working.
Booting back to previous kernel, touchpad is working perfectly fine.