This only happens , when I win wars. This is kinda shit , because after I win these I just can give up my game.
I think I know what's going on.
Do you, by chance, have the Land Appropriation policy active?
You see it's changed in a very significant way in 2.2. Instead of simply making sure there is free space for your own pops on conquest, it always removes 5 of their pops...
...And moves five of your citizen pops to take their place.
Per Planet.
Unless you are enslaving the whole lot of them (moving them all to worker jobs), or have a significant number of unemployed pops, conquests of more than one planet will cause a *massive* downward shift on your basic resource income, as worker pops leave your planet to often take specialist or ruler jobs at your freshly conquered ones.
If you plan on conquering your neighbors, I recommend turning that off until you have full grasp of the new economy.