Why does Ubuntu "think" for a long time after installation?

Question

ubuntu

If you run it without installing it, everything flies perfectly ...
But after installation, it even starts for about 15 minutes (by the way, the installation also takes a very long time, almost 2 hours) and it takes about a minute to load even the settings window or the application menu. It is hardly connected with the video card, since after loading the windows are easily and smoothly dragged, and the re-opening is instantaneous. I tried probably all the tips that were in the search engines, can you tell me a magic command here that will fix this?
I checked the memory for errors (both the RAM and the disk and the flash drive), tried different file systems and versions of ext, after installation I tried to disable paging from the disk / from the flash drive, I tried to install only on the flash drive (I removed the disk altogether), after installation I cleared the cache, updated system, tried to install a proprietary driver on the video card, tried to find errors during startup / installation ... in the end, it still thinks for a very long time.
Hardware specifications: AMD A10, 4GB DD3 and ATI discrete card, don't remember the model.
Tried Ubuntu 16.04 x32 and x64, and the recently released 18.04 x64.

Answer 1

dmesg