Random keyboard input and mouse not working

Running F24 latest kernel on a Thinkpad T15 Gen 1, XFCE 4.20 and an external Lenovo monitor attached.

From time to time, I am getting random freezes of (1) keyboard input (either nothing works at all, or random letters stop working e.g. yesterday Shift-c didn’t work for a while, but if I put Caps Lock on, I would get a C, (2) I am unable to move or resize any windows (but can minimise and restore any apps with just a single window only), and (3), no menus appear (applications or XFCE) from a left mouse click, but a right mouse click does bring up a menu.

The behaviours usually clear themselves after waiting a number of minutes.

Anyone else seen this, know what’s going on (and how to fix it), or where to look to investigate the cause.