Addons randomly disabling

Addons that I have in my worlds have been randomly disabling. This recently happened with the essentials addon, the game crashed and then when I loaded back into the game, all of my addons had jjst disappeared(more tnt, gravestones and essentials). I lost all addon items and blocks, even when I re-enabled the addons. This is not the first time this happened. When addons were first released, I created a new survival world with all the free addons. Only soon after creating the world, I logged back in and all the addons were gone. Please fix this.