While mining in Realms I have had 3 tools vanish on me. One was equipped and in use, the others were just in my inventory.

The one that was in use was a Diamond Pickaxe, enchanted with Unbreaking III, Silk Touch I, and Efficiency IV, if that matters. It went from a working pickaxe to a stack of 28 Wheat right before my eyes. It was brand new, maybe 40 blocks mined. The other two were an enchanted Diamond Pickaxe (Fortune III) and a Shovel (Silk Touch I, Unbreaking III, Efficiency III)

This seems to be just with the new 0.16.0 recent client. I do not plan locally on my phone, just on Realms.