Yes, I tried that at first and it didn’t work. Played around and figured that before applying the expression, opacity must be the same value as the first keyframe of “leader”… in my case – 0%.
Just found a solution. It turns out that it was motion blur’s fault. It was enabled for separate layers but not for the composition. So when rendering through Render Queue it automatically turned Motion blur on for checked layers.
Anyway thanks for trying to help Anthony!
Saving the RAM preview works, everything looks as it should. Also I tried to render through Export and it worked there as well, so it looks that the problem is in Render Queue.