That seems like extremely overpowered (quadrupling my science), so I the suspect it is some kind of bug. I would expect the osmosis to happen fewer times.

If it helps anything I there is an intense culture split in this game, so it may have something to do with that. Otherwise I have no idea why this happens.

To reproduce just load one of these save files and see it re-occurring until you end the game.

auto-save 952.ctr

auto-save 953.ctr

auto-save 954.ctr

auto-save 955.ctr

Edit: Some, some cities do actually not get the event on some turns, my main city with a 1/3 split with 3 cultures does get it every turn.