mouse / keyboard input oddity

[R Kimber]

Since upgrading to Ubuntu Mate 17.04 I've experienced a slightly irritating
problem. After a short period of inactivity (not sure how long but <30
mins), when I return to the PC a mouse click or a single key press will not
achieve anything. Keyboard input is accepted on the second key press, and
mouse clicks are accepted only after I have pressed a key on the keyboard.
Ctrl-F (say) seems to work immediately, however.

Has anyone else experienced this? And is there a simple solution?

There is a similar situation when I try to log in. I have it set so that I
can log in without a password.  This worked fine with 16.10, but with 17.04
I just get a blank Ubuntu screen (i.e. just a logo) and nothing happens
until I press a couple of keys.

It's not a mega problem, but it irritates :)

- Richard.
-- 
Richard Kimber