Items in your offhand don't visibly update their durability or do the item swap movement animation when using the mending enchantment while you have a chest or other inventory opened that doesn't show the offhand slot.
The items still receive experience and durability properly, but it isn't reflected in the hotbar slot until you close out of the chest or use the hotkey to move the item out of your offhand.
Other than the durability bar, this is also noticeable when using a resource pack to give tools different textures when at different durability levels. The texture isn't updated while the offhand slot is hidden while viewing another inventory.
Linked issues
Comments 2
Thank you for your report!
We're tracking this issue in MC-152526, 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
-- I am a bot. This action was performed automatically! The ticket was resolved by one of our moderators, and I left this message to give more information to you.
Duplicate of MC-152526.