This might be working as intended, but the AI for spiders gets stuck on the ceiling while trying to climb the walls and does not come down or attempt to attack players. That is to say, if the spider is attempting to scale a wall to climb over it, it will reach the ceiling and stay on the block where it reached the ceiling without moving, coming down, going left or right, or attacking the player.
Thank you for your report!
We're tracking this issue in MC-154160, so this ticket is being resolved and linked as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
If you haven't already, you might like to make use of the search feature to see if the issue has already been mentioned.
Quick Links:
📓 Bug Tracker Guidelines – 💬 Community Support – 📧 Mojang Support
📓 Project Summary – ✍️ Feedback and Suggestions – 📖 Game Wiki