/locate still a bug for Mansion and Desert Temple as of 1.13 pre 5 - It will lag tremendously without giving coordinates then eventually crash.
I was having the same problem in 1.11.2 for awhile, but I think I fixed it when I placed a shulker box next to the bed on the left at the top part of the bed. I have blocks on the right side and front of the bed acting as walls for my house, a one block space between the foot of the bed and a furnace, and open blocks to the left at the bed at the bottom. I have a two block space above the bed for my ceiling.
Maybe it has something to do with putting a block next to the top part of the bed on each side? Not tested, just a possibility. Hope this helps.
I LOVE this - if it is a bug it should stay that way!