Ubuntu: Mouse stops responding to clicks when editing PDF

[Flarup]

I have a PDF file created from Autocad. It has a lot of details.
When I open the PDF file in libreoffice draw, it shows fine, but when I start to select chunks of the drawing, Libreoffice goes grey, and goes to 100% CPU load on one core.

Fair enough, it is a lot of data, but the Mouse stops responding. I can move it, but when I click on another application, nothing happens.

I can change focus to another application with Alt-Tab, but the mouse is still not responding. It is like the mouse clicks are not detected.

Version: 6.4.6.2
Build ID: 1:6.4.6-0ubuntu0.20.04.1
CPU threads: 8; OS: Linux 5.4; UI render: default; VCL: gtk3; 
Locale: en-US (en_US.UTF-8); UI-Language: en-US
Calc: threaded

Display manager: gdm3

[anon73440385]

Ubuntu 20.04 and LibreOffice :6.4.6-0ubuntu0.20.04.1 (from Ubuntus repositories) => My guess: This is a initial install of LibreOffice and you face another incarnation of a huge variety of problems with initial installs of LibreOffice on Ubuntu 20.04 based GNU/Linux distributions.

Please check: https://ask.libreoffice.org/t/cups-authentication-not-working-correctly/57731 and the further **References** provided in my answer therein.