Orientalist said:
Jim Culver, the Jazz man extraordinaire, jumped, on purpose, through one of the 4 Gates. Other World Encounter. Pass a Speed - 2 and return back to Arkham. So Jim returns to Arkham at the end of his first Other World Encounter. Since he had a lot of clue tokens, he is trying to seal the Gate. Gulp - he fails. So he remains on the Gate and he will try to seal it next turn.
Next - Mythos Card Phase.
Oh gosh, a monster surge. To keep things easier to explain, a monster appears on the Gate where Jim Culver is. What exactly happens now?
Jim will try to seal once again the Gate next round. He fails once again.
Will he now deal with the Monster on the Gate?
Or he must deal with the Monster before trying to seal the Gate once again?
First of all, if Jim returns to Arkham as a result of an OW encounters, he is not allowed to seal the gate immediately. Remember the sequence:
Phase 1 - Upkeep
Phase 2 - Movement
Phase 3 - Arkham Encounters
Phase 4 - Other World Encounters
Phase 5 - Mythos phase
He returns to Arkham during Phase 4, he can try to close / seal only during Phase 3. So he is not allowed to try until the next round
So, Mythos Phase -> monster surge and then a new round begins
In the new round, he can try to seal / close the gate, but this could happen only in Phase 3. In Phase 2, Movement, he has to deal with the monster(s) arrived via monster surge. In case he successfully beat them, or escape from them, he now can try to seal / close for the first time
Hope this helps!