Lightroom Classic uses it's content disk excessively during several minutes

Lightroom Classic uses the content disk excessively the first couple of minutes when starting up. It seems to look for images. This causes the program to be unresponsive and unusable for several minutes after starting it. 

How to reproduce:
Start Task Manager and note the disk usage. 
Start Lightroom Classic (I use an old school hard drive, not SSD, and most images except for the last two years are in the catalog are not present).

Expected result:
The disk usage should be within acceptable levels and the program responsive.

Actual result:
The disk goes up to 100% usage for several minutes, causing unresponsiveness for several minutes. Selecting any other image than the one displayed since last last session does not work. The import function does work, but trying to edit any images is impossible.