Occasionally, I find duplicate enchanted books in treasure chests. I long suspected this issue, however, the results so far have been plausible for random luck, with the books having one or two enchantments. This time, I have found two books in the same chest with enchantments:

• Aqua Affinity I
• Looting III
• Power IV
• Lure III

The chest in question can be accessed within the stronghold in the bug MCPE-19526. It is in the library that is located in the stronghold wing, that is hidden behind the first walled off section (See other bug for more info).