Some players report that when they launch the game they get mini freezes (< 1 second) every few seconds (~2) for up to 5 minutes after launching the game. It also occurs when no mods are running.
And this problem doesn't happen when they launch the game (and Steam) offline.
I personally don't have this problem but since I didn't find anyone reporting it here (they simply complain about it on Discord) I decided to at least make a ticket for further investigation.
Since the problem occurs when the users are online, I guess it is related to one of these:
1. BattleEye
2. Steam Updating in the background (though people said this wasn't the game)
3. DLC "Ad"
4. A3 units
In my case (where problem doesn't occur), I:
1. don't run BattleEye
2. have all DLCs
3. don't use A3 units
So I guess any of them can be a valid cause of the problem.