Having many Addons and Texture packs active produces a texture error that turns the UI and blocks magenta. This has been a noticeable issue since April when Add-ons were introduced. It has became more unreasonable when we pay for access to these packs exclusively just for them to make the game unplayable.
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We're tracking this issue in MCPE-180342, so this ticket is being resolved and linked as a duplicate.
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They are encrypted to prevent private server use and piracy. If they are able to integrate them with Server hosts other than realms it might help alleviate the problem as i believe it is a resource allocation problem with realms.