To reproduce: make a hole that is 4 by 4 by 4 blocks big, then put blocks that align the ghast to go right in.
What originally happened and is expected: the ghast fits easily and stays there.
What actually happens: the ghast doesn't go in no matter how much you push, and even if you force it in using mobs or pistons, the ghast will suffocate and die.
Thank you for your report!
We're tracking this issue in MCPE-221320, 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 (Technical Issues) – 📧 Microsoft Support (Account Issues)
📓 Project Summary – ✍️ Feedback and Suggestions – 📖 Game Wiki