I had stopped playing the Bedrock version for X Box One because my map had so much lag I couldn't even break a dirt block. I have found the cause of the lag.

I have a villager breeder that when there are more than ten villagers does produce an Iron Golem. When this happens my map has periods of extreme lag. If you go to the breeding center and kill the Iron Golem the lag is instantly gone. I stay within 120 blocks of the breeding center because of the seed put the world spawn point on a small island. (seed -1107795658)

Every time an Iron Golem spawns in the breeding center there is extreme lag, however, I don't seem to have as much problem from the Iron Golem farm because of it's short life I guess.
This world is 100% survival and never has had cheats turned on this world. No mods, texture packs or skin changes either. 100% vanilla.
I've tried rebooting the console, unplugging and letting it cool completely but the lag remains when there is an Iron Golem at the breeding center.

As an interesting note - if you put the villagers in the breeding center in boats so they are not moving around there is no lag, however, I can't tell if it's them moving that is causing the lag or the Iron Golem moving because he usually gets in a boat too. (Didn't think they could do that be they can)

Hope you can recreate this and fix it. Gets to be a bother running back to kill the Iron Golem all the time. (Do have 9 stacks of iron from the breeding center) Always a bright side.