Thumbnails first generated at first look into folder

[Thomas Hannibal]

Version 7.2.0-rc
Macbook pro - Big Sur
Two albums: External SSd disk + NAS

Problem:
It seems like the thumbnails is forst generated when I enter an album folder first time. The thumbnails is showing up one by one in a slow rate. Next time I enter they show up significantly faster.

I have tried to use Tools > Maintenance > Rebild thumbnails. The result is the same. I need to go into each album and let the thumbnails be generated. I have just added 70000 images and several hundred folders.

Any suggestions how to force generating of the thumbnails?

[Thomas Hannibal]

Here is a fix:

It is possible to for thumbnail generating, if I select all the  folders in the Tools > Maintenance > Rebild thumbnails. It is not enough  to select the top folder - I have to unfold the folder tree and select all sub-folders to make it work.