Rewinding with Portal Vanguard is resetting Ceaseless Expanse to its mana cost before the enemy turn. Ceaseless starts playable in my hand but after playing Portal Vanguard with its rewind effect has its mana cost increased as if it was before the enemy turn, sometimes jumping 10+ mana.
We’ll have a look, thanks Wattzy. 
If by any chance you have a replay of your game, I’d appreciate if you could upload it somewhere and add a link to it here.