sphinx of the second, thrid, fourth, fifth...
If you copy sphinx of the second sun you somehow get a another combat step and the more main phases ad infinitum
Happened again in Event # 241644728. Infinite loop of combats and turns.
Still bugged, another example:
The issue is this ruling:
"If you somehow have more than two main phases in a turn, each main phase other than the first one is a postcombat main phase, and Sphinx of the Second Sun’s ability triggers at the beginning of each of them. (2020-11-10)"
It looks like the game returns to the pre-combat main phase, followed by a combat phase and a post-combat main phase where the sphinxes trigger again.
Can confirm. With a copy in play, your turn just keeps going back to the first main phase and never ends.