Remove the base cover and check the condition of the battery.  It's right below the touchpad, and erratic behavior is often the first sign of a battery beginning to swell.  If it's at all swollen, remove and dispose of it outside your home or office, immediately.  Then order a replacement -- the system will run fine on AC power until the battery is replaced.

The trackpad clicks feels perfectly fine (except for a <1mm jiggle during the trackpad's resting position), it's just sometimes it doesn't register the clicking. There doesn't seem to be any pressure pushing up onto the trackpad at all. I'm pretty sure this is just a trackpad issue.

If so, note that you cannot replace just the touchpad on this model -- you must replace the entire palmrest-keyboard-touchpad assembly:

https://www.parts-people.com/index.php?action=item&id=35298

Since this requires a total system tear-down, it would still be a good idea to rule out the battery as the cause before buying the part and taking the hour+ it will involve to replace it, particularly given that the battery will need to be removed as part of the repair.

Service manual here:

https://www.dell.com/support/home/en-us/product-support/product/xps-15-9500-laptop/docs

@ejn63​ Late reply but I stumbled upon this answer because I've got similar issues regarding my trackpad. In addition, my battery was also not holding any charge so I decided to give this a shot and lo and behold, my battery is swollen! Thanks for the tip!

As a bonus, I managed to get a hold of an even higher capacity battery vs. the one that came from factory :D

@buntro23_​ hi there, where did you get your replacement battery?