Different auto-complete formats. Why?

[ubaldot]

I noticed that I often have two different formats during the autocomplete.

Format 1:

Format 2:

The preview happens only when suggestions appear in the form of Format 1.
If it may help, I only have pylsp enabled as linter and I have

let g:ale_completion_enabled = 1
let g:ale_completion_autoimport = 1
set omnifunc=ale#completion#OmniFunc

in my .vimrc before loading ALE.

It seems to me that Format 1 is triggered by Vim omnicomplete, whereas Format 2 is triggered by pylsp.
In-fact, I tried to set both let g:ale_disable_lsp = 1 and to don't load ALE at all and I get both times Format 1, meaning that the builtin Vim omnicomplete works reasonably well.

But what should I do if I want to use pylsp instead?