After throwing the trident, the shield will no longer block the attack.
This problem can be solved by eating food or re-entering the world.
It occurs with or without behavior packs and regardless of whether it is multiplayer or not.
Some people have reported the same problem in the nether, but this problem also occurs in dimensions other than the nether.
Video: https://mega.nz/file/yAsXiD4b#pdVCkewepgXxF1mV_T1_5T4KsAQkz5PCFO-cR1qGzF8
Thank you for your report!
We're tracking this issue in MCPE-171346, 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