Missing task. (The Elder Scrolls 4: Oblivion)

I remember I had assignments about the Gray Fox and the Vampires. Today I went into the game and found that these tasks were missing. Is this somehow related to the completion of the main quest (Defeating Mehrunes Dagon)? I completed it completely yesterday. Started rummaging through assignments. There was a task about finding a thieves guild (secret note). I started to do it. They mentioned the Gray Fox. I remembered that there was a task associated with him. And he is not there. And the vampires were gone. Why? I cannot find the reason.