The bug

Placing large numbers of Banners in a world quickly causes performance issues. This can happen with any Banners with or without patterns, although the performance issues seem to happen more quickly if the Banners have patterns on them.

Steps to Reproduce

1. Create a new Creative Superflat world with structures disabled and all spawning gamerules set to false.

2. Obtain a Banner, a Loom, and six dyes from the Creative Inventory.

3. Use the Loom and dyes to apply six patterns to the Banner.

4. Press F3+2 to show FPS and TPS.

5. Begin placing Banners in the world.

6. Notice how the FPS gradually drops as you place more Banners.

Expected result

Banners would have a relatively small impact on game performance.

Actual result

Banners have a significant impact on game performance.