I am having the exact same issue with an Acer 714 a Phillips non-touch display and an innocn touch display. Did you ever find a solution?
Weird it totally worked for me. As soon as I calibrated the external monitor everything was ok. It also did not give me the option to calibrate the internal screen which is fine. Also I have the external touchscreen set up as the primary monitor. That may help.... and I am on the beta channel for chrome. Try changing those settings and re-calibrating and restarting.@AsherF - thanks for the pointer, but did you get this to work fully? I have turned on the flag, restarted my ChromeBook (so it takes effect) and, with the two external monitors attached - one touchscreen and one not, I calibrated my external touchscreen monitor.
The dots appear towards the corners of my external touchscreen monitor as expected. I tap each one in turn with my finger and when it says it is calibrated I Escape out. However, when I then try to use the touchscreen capability of my external touchscreen monitor the ChromeBook still thinks I am touching the internal touchscreen display.
I do not get the option of calibrating my internal monitor and, whilst it gives me the option to, there is no point in trying to calibrate by external non-touchscreen monitor. So I am still facing the same problem - with both a touchscreen and non-touchscreen external monitor attached to an Acer Spin 713 I am unable to use the touchscreen capabilities of the external monitor. The moment I disonnect the external non-touchscreen monitor then the external touchscreen monitor works just fine.