Just wanna add my stupid experience)) But it 100% reflects all sympthoms and visual issues discribed above))
So I was trying to alighn 2 objects by their origins, I've set both origins 'to geometry', then selected both objects and tried to alighn them on X and Y axis by pressing 'S -> X -> 0 and S -> Y -> 0

I don't know if the hot keys were wrong or they changed from the version of the tutorial but everything dissapeared))) Then I understood that objects just collapsed in ONLY 1 point. So I was able to see them in the outliner and in 3D viewport actually (but I thought it was the origin point, but it were my objects scaled down to 1 point);