The Silph Co. 11F lift blocked exit glitch is a continuation of the Silph Co. 11F above lift door glitch in Pokémon Red and Blue that was documented by "landon morrical".
If you get to the lift on Silph Co. 11F without using the "Which floor do you want?" prompt or without entering it from when you are already standing on the elevator door (by exiting the lift once), then the left exit will be blocked if you do not move.
This glitch is similar to the Mr. Fuji's house door glitch and Map hex:99 house door glitch.
This glitch appears to have been fixed in Pokémon Yellow.