switchInDirection() hotkey doesn't work

I'm synergy user for years, and I've always used this hotkey setup:

keystroke(control+alt+right) = switchInDirection(right)
keystroke(control+alt+left) = switchInDirection(left)

(setup with one client on the right)

I never had any problem with this. But one day in my office switchInDirection(left) just stopped working (going back from client to server). I can go right to the client, but I can't go back with the shortcut.

I think I've tried everything. Change keystroke (shortcuts), change switchInDirection() to switchToScreen(). I always can move to the client, but come back only using mouse.

My theory is, that the client (laptop) is not registering global shortcut. But if I move back home and connect it to a different synergy server it works perfectly.

So my question is: how to approach this problem? I have no idea how to debug this.