Whenever I attempt to use an Add-on purchased on the marketplace on a new and/or existing world, the addon will fail to load and a bunch of errors will continuously appear on screen. I was able to grab one screenshot which has been linked below as each error was going by too fast to see. I tested 3 separate addons, together and alone. These Addons are as follows:

• World Builder
• Essentials
• All the Wool

The creator for Essentials has been notified, just in case this is a coding error on the creators parts. However, as its multiple, I assume its a base bug.

Edit: The bug also covers third party addons from sites such as MCPEDL

Edit 2: These addons did NOT require holiday Creator features and ran perfectly well without the.m. The three addons I tested are stated above with them all being by separate creators and unconnected. For each, the exact same errors occured. Extra info that could help: No items or textures that are added in each add-on appear in either commands or the creative inventory. 

Final Edit (16.08.24): The latest hotfix (1.21.21) has fixed the issue.