I just took a screenshot with the updated Grab app in MacOS Mojave and my 4-finger swipe to switch Spaces desktops stopped working. I found this post which talks about something similar with multitouch gestures which sounds like it’s a randomly occurring issue with multitouch gestures. A reboot fixed it for me, but it was surprising how much I rely on gestures to switch desktops/apps, and when it’s not working how to you switch?! (Ctrl-Left/Right is also works as a keyboard shortcut).