After deleting a world with an Add-On in it, I was unable to use add-ons in new worlds. However, downloading worlds with pre-installed add-ons worked just fine.
MCPE-17619
Unable to use Add-Ons after deleting a world!
Resolved
Works As Intended
0
You will need to keep a backup copy of the add ons as they are saved in each worlds folder unless added as a global resource.