Same here. All users on my Realm playing via Windows 10 Beta version or MCPE experience this. I have been able to replicate it in single and double chests most of the time. Sometimes it doesn't happen, a couple times I get extra items but most of the time items are lost.
I have experienced this in my Realm, as has my wife. If a wolf gets wet from rain or a water block it will make the sound for shaking off water in a loop. The sound doesn't stop even in broad daylight unless you avoid that wolf or kill it. Even if it is turned to your dog it continues to make the noise. We killed off our wolves because the noise was so loud we couldn't hear anything else in the game.
Myself and players on my Realm are experiencing the same issue. Double chests will break but items inside will be lost. Not always the case but when I load a double chest there is a small chance of dropping more than originally inside and a higher chance of it not dropping anything at all. We experimented with splitting items across both ends of the chest, stacking all on one side or the other, and breaking each side in each scenario. The results were mixed but most of the time the items disappeared altogether, sometimes some or all dropped and a couple times the number increased.
I have experienced this now on both Windows 10 Beta and MCPE. Had it happen yesterday in other biomes. Also found it was random. I was in several areas for a few day/night cycles and some zombies/skeletons would burn in daylight and some world not. Again, no armor/helmet I them.