I am experiencing something like a 1-3 second lag only when side-swiping with 3 fingers between apps/desktops.
However, if I first swipe up with 3 fingers to enable mission control, then everything is fine and I can swipe between desktops seamlessly.
I've noticed that if I run 3 fingers across the trackpad, then I'll eventually be able to switch between desktops. At that point, if I keep the motion going I can switch between multiple desktops.
Any suggestions welcome – I've changed my display color profile and reset my nvram as other mojave threads have suggested.
EDIT: Changing my energy saving preferences to only use the dedicated graphics card doesn't show any differences. Using Mojave in light mode instead of Dark mode doesn't change anything either.
EDIT2: I've discovered that switching user accounts completely resolves the issue.
Best Answer
Posting this as an answer so that it's more visible.
I'm going to detail exactly what I did even if the steps seems unnecessary.
I switched between the two accounts a couple of times, noticing that the 3 finger side swipe between spaces wasn't working on my normal account but was working on my test account. I decided to duplicate my normal account and was reading about how to do this on my test account. I started up the migration tool and went through a couple of steps before running into an error. At this point I switched back to my normal account and the swipe was working again.