Played a game where upon trying to cast spells, the timer would run out, causing the spells to become stuck on top of the stack.
The game would continue, but any triggers, abilities or other spells would seemingly go into the stack below the stuck spell..
I am unable to access the spell in any other zone, so the game seems to treat it as though it does not exist.

This happened twice, upon the second time doing so, the new stuck card replaced the older one, but neither were put into any other zones.