How to avoid becoming LibreOffice calc becoming slow?

I am using LibreOffice calc on Ubuntu 16.04.6, and when I start (or restart) LibreOffice calc it is fast, without noticing any delay when I click in different cells, for example.

However, later it becomes very slow. When I then click in some cell it takes about 1 second until the focus is changed. It does not sound much, but when you have to select an area of cells it becomes a very difficult task as the LibreOffice reaction is so slow.

I already tried suggestions I could found for settings in “Tools → options”:

  • LibreOffice → Memory: Increasing memory per object to 20 MB
  • LibreOffice → View: Using/not using OpenGL
  • Load/Save → VBA Prpoerties: Disabling everything on this page

Is there anything else I can try?