I have a similar issue, except I was able to get everything, talk to Poseidon and he gave me the WaveCutter power. However he told me to swim over and check on Hades, then disappeared and now the quest objective says "Convince the gods to return to Olympos 3/4" but there is no map marker, and if I go to the spot it should be, he's not there. I have uploaded my save to the cloud
So I'm not sure if you devs fixed it, but Poseidon and the mission tag on the map are working. I finished the last vault for Hades, and he asked me to talk to poseidon. So that activated an objective tag on the map over poseidon, and I was able to talk to him and start the date with destiny objective.
If you fixed it, thank you! If not, the issue might be that Poseidon is showing up sooner than he is supposed to instead of for the quest after Hades.
I don't have the exact date yet, razvanrazy! I'm sorry about that. When the patch containing the fix is live, we'll have patch notes available in our General Discussions area in a stickied thread, as well as information on our Immortals Fenyx Rising blog. You are certainly welcome to leave a review about your stopped progression. We understand that negative and positive experiences are both very important and it allows us to grow as a company and continue improving the game.