Manual Land Tap Bug
Whatever game I was in at around 3:52 PM (PST) (the second game after I was promoted to Diamond Tier 4), my land was specifically tapped for use manually, then I activated an ability of a land I controlled to turn it into a creature to block an attacking creature. For whatever reason, the program then tapped me out completely and drained my mana pool during the combat phase even though I had plenty of mana to cast an instant that cost 1 white and 1 black mana which was in my hand to exile a second attacking creature in order to prevent losing the game to combat damage. Because the program glitched and tapped me out and drained my mana pool, I was unable to exile the second attacking creature and therefore lost the game through no fault of my own.