World comp issues

Working with just terrain nothing else, I’m getting weird distortions if that’s the word, one of my terrain tiles, as seen in world comp view, see below:

https://1drv.ms/u/s!AvVOuPY0RaB5hekHg8nEAC5IQTHMgA

As seen on left one tile is very large, ( although in play, depending where I am in world, large sections of playable world are invisible ( likely streamed out ?), yet on the right, #3 is almost twice the size of the other 3 ( as on left side ) - what would have occurred to allow this,is this a bug or a wonkie value I have ( or none) I have for streaming ?

thx anyone