Don’t think this is related to the application, because the focus gets locked on different applications at different times: IntelliJ Idea, Firefox, gterm, …. When the focus is locked, if I try to move or resize any window it will move or resize only the window to which the focus is locked.
It happens at random – I don’ think its some key combination I’m pressing. But I will watch carefully to see if that is the case.
I’ve tried pressing modifier keys, and combination of modifier keys but it doesn’t unlock the focus.
There was a similar issue with an earlier version of NoMachine (see https://www.nomachine.com/TR12K04101). There the advice was to try running ‘xdotool key XF86Ungrab’. I tried that, and it seems to work sometimes but not always.
It does seem to be related to the bandwidth of my connection. If I am hardwired to my router it almost never happens. If I am connecting over WiFi it happens all the time.
Disconnecting and reconnecting *always* fixes it (for a while).