Hi rezzuka, welcome to the forums,
I’m sorry to hear these issues are affecting your game.
With regards to loading into a save with the incorrect person. Do you recall what screen you were sent to when you disconnected from the game and did you attempt to rejoin while your friend was in the opening sequence or before? Could your friend see you before you were joined with another player?
With regards to no interactions, incase you have not seen it, I have a post on the issue here: [Known Issue][PS4/XB1] Loss of interactions which I updated recently as the team believe they may have found the cause of the issue and are working to resolve it.
When playing with your friend, before you lost the interactions, one or both or you traveled to a nearby island? If so, was it an island with cliffs? and have you at any stage lost creatures through the sand after hunting them?