I tried searching and could not find any issues reported like this for 1.9. I'm also not sure whether this is a Xbox One issue, or a Realms issue. 

After updating to 1.9 I logged onto my Realm with the Windows 10 Edition, my inventory loaded fine as well as everything else. Moments after my girlfriend, sitting next to me on her Xbox, logged on. She didn't die, or sky-fall from spawn like many of us have had happen, but rather, everything in her inventory was just gone. Lots of end game gear, shulker boxes full of stuff, max enchanted weapons, etc. 

I have one other friend who plays the realm on Windows 10 Edition. He has not been on since the update but when he does, if he loses his inventory as well I will know it's a Realm issue, but as of now I'm assuming it's Xbox One since I was not affected on Windows 10.