Items from the end of the run can indeed have a chance at corruption. That mechanic went live with the start of patch 8.3 so even though the season just started, it’s possible to get corrupted items since 8.3 went live.
Also the whole no cloaks thing is only for the weekly Mythic + chest. They should still have a chance to drop from the dungeon chest at the end of a run and they can still pop up in Warfront loot too.
Hope that helps clarify those three points 