I have just run into a recurrence of this particular problem, and found an obscure post which seems to have helped my issue:
My laptop also has a touch screen (which I never use) and this is interpreted largely in the same manner as the touchpad. There seems to be some conflict in the 'disable-while-typing' routine, and I found that disabling the touchscreen fixes the issue. There is an open bug report on this issue at https://bugs.launchpad.net/ubuntu/+source/gnome-shell/+bug/1733032
Run the command xinput
to list your devices. Mine output is
xinput
⎡ Virtual core pointer id=2 [master pointer (3)]
⎜ ↳ Virtual core XTEST pointer id=4 [slave pointer (2)]
⎜ ↳ Logitech M315/M235 id=9 [slave pointer (2)]
⎜ ↳ SynPS/2 Synaptics TouchPad id=14 [slave pointer (2)]
⎜ ↳ ELAN Touchscreen id=10 [slave pointer (2)]
⎣ Virtual core keyboard id=3 [master keyboard (2)]
↳ Virtual core XTEST keyboard id=5 [slave keyboard (3)]
↳ Power Button id=6 [slave keyboard (3)]
↳ Video Bus id=7 [slave keyboard (3)]
↳ Power Button id=8 [slave keyboard (3)]
↳ Dell WMI hotkeys id=12 [slave keyboard (3)]
↳ AT Translated Set 2 keyboard id=13 [slave keyboard (3)]
↳ Laptop_Integrated_Webcam_HD: In id=11 [slave keyboard (3)]
In my case, I found that disabling the 'ELAN touchscreen' with the command
xinput set-prop 10 "Device Enabled" 0
has caused the touchpad to behave in the manner I expect - namely that the device is disabled while I am typing and my palm or wrists brush against the touchpad.