Some trackpad gestures, especially 'Spaces', unusable

This is since Yosemite. Some trackpad gestures are slow and laggy, but the worst is what used to be called Spaces and is now 'swipe between full-screen apps'. If I invoke that, nothing happens except that all computer function except mouse movement stops dead, then maybe 10 seconds later the screen will attempt to shift but get stuck between two desktops. Eventually after a great deal of swiping I can get it back to some semblance of usability. Mission Control is almost as bad.

I just tried booting into a new user account to test it and everything works as it should. In particular I noticed that Mission Control was beautiful in that it only showed two desktops at the top. Normally I see 138 minuscule desktops in the band at the top, which is obviously idiotic.

So it's a software issue. I have 22 login items and tried disabling the ones that I thought might be responsible; they weren't. I then did a safe boot into my user account and the problem was slightly improved but still present. I have tried deselecting all trackpad gestures, restarting, re-enabling and restarting. No difference.

Where to go from here?