Description/How to reproduce:

I can't recall the exact circumstances, around turn 160, I started suddently having turns were multiple cities would have "osmosis events". When I tried to get more informationby hovering or  clicking on the icons the reward was said to be zero (don't remember the exact wording but basically an emty reward). Happend on multiple rounds until the end of the game.

Indeed, i have seen these too, on the top ("Humankind") difficulty level.  Osmosis events that do provide a rewards seem to occur more frequently than these zero-reward events, but amounts of zero definitely occur now and then.

Unfortunately, i can't say either when exactly that happens.  The player does not initiate osmosis events in the first place, they just happen...

The only hint i can provide is that zero-reward Osmosis events usually happened close in time to events that did provide rewards, like in the same game turn or the turn before or after.  But i'm not sure that's always the case.