In my world (seed 7423936397741743481) there is a cave spider spawner at 906/28/501 xyz, where every cycle some of the spiders created spawn inside the stone walls of the tunnel. After being spawned the spiders quicly die to suffocation and their drops fly on the tunnel floor. Confirmed in separate creative and survival worlds. The issue persisted even after clearing the cobwebs around the spawner to ensure valid spawning spaces.