Game skipped my second main phase after attacks.

My life gain from attacks solved my "Case of the Uneaten feast", but the game immediately skipped to my opponent's draw/upkeep without allowing me to solve the case and cast from my graveyard (untapped lands were available).

Oddly, a permanent of his triggered something at his upkeep and i was able to activate the Solved case as a response to it during their turn's upkeep - but i was not able to cast any cards despite their ghostly presence in my empty hand.