Copper Bars seem to Z-fight with blocks on the bottom, such as Prismarine Bricks.
Note: This is easier to see when looking above from a specific angle.
To recreate this bug, you need to get any kind of Copper Bar block and place it above a Prismarine Brick block.
Thank you for your report!
We're tracking this issue in MC-192420, 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, please make use of the search feature to see if an issue you are about to report has already been reported.
Quick Links:
📓 Bug Tracker Guidelines – 💬 Community Support – 📧 Mojang Support (Technical Issues) – 📧 Microsoft Support (Account Issues)
📓 Project Summary – ✍️ Feedback and Suggestions – 📖 Game Wiki