Dear,

have you tried to apply the Trackpint firmware update ?
https://pcsupport.lenovo.com/us/en/products/LAPTOPS-AND-NETBOOKS/THINKPAD-X-SERIES-LAPTOPS/THINKPAD-X1-CARBON-TYPE-20HR-20HQ/downloads/DS122148

The problem was solved by Lenovo Technical Support Service.

They detected that it was a hardware problem, so they changed the complete tocuhpad. The technician took a couple of hours to change the part and now both the tocuhpad and the trackpad work without problems.

I recommend contacting Technical Service if the problem arises, since after updating drivers and other solutions raised in the forum, the problems were solved only with the change of the piece.

I received my X1 Carbon 5th Gen laptop in early October 2017. Overall, I would say this is a great laptop - EXCEPT for the touchpad.  I fully echo the frustration and disappointment expressed in your post.  I am a professor of medicine and this laptop is the center of my professional research life. Since switching over to the X1 Carbon 5th gen, I find myself wanting to throw the thing across the room anytime I have to use the touchpad - that, or take my fist and pound the the $%#* out of the touchpad.  Like your post says, the touchpad will jump, will not respond to a slight shift in the finger's movement, only to then over compensate and jump far a second or two later. For example, if you're working in Microsoft Word and trying ot resize the width of a column in a table (or the height of a row), you need to put the mouse arrow over the column until it turns into the "width adjuster" double-arrow ... well, with this $1800 X1 Carbon, good luck doing that without having a complete mental breakdown.  You get the cursor near the line only to have it JUMP right past the line.  Then you move it back the other way and it won't move at all, only to leap past the column line a second later. I've adjusted the sensitivity settings and I'm using the latest drivers - and there has been zero improvement.  My previous laptop, a ThinkPad T460s, had an FLAWLESS touchpad.  Never had a single problem with the T460s.  Now I find myself wanting to put the X1 Carbon in the garbage bin ... all because of something that should have been identified and resolved by Lenovo BEFORE putting the 5th gen on the market.  

If this is a hardware issue, then Lenovo has got to recall these touchpads and install new ones THAT WORK.  If it's a software issue, then they need to get a fix pushed out to everyone YESTERDAY.  If this is not resolved, I guarantee this will be my last ThinkPad or Lenovo purchase.