I'm having the same issue in my Realm on Windows 10 and the Xbox One editions. It appears that, when at sea level, I can't place a door - there is a flicker and the door returns to my inventory. The only workaround I found is to set a block above sea level, place a door, and have a stairway on each side of the block that was raised up.
See screenshots - screenshot-1 is the result of trying to place a door. screenshot-2 is the only way I was able to place a door. I will also attach a screencast if that helps to get the issue resolved.
I'm having the same issue in my Realm on Windows 10 and the Xbox One editions. It appears that, when at sea level, I can't place a door - there is a flicker and the door returns to my inventory. The only workaround I found is to set a block above sea level, place a door, and have a stairway on each side of the block that was raised up.
See screenshots - screenshot-1 is the result of trying to place a door. screenshot-2 is the only way I was able to place a door. I will also attach a screencast if that helps to get the issue resolved.