For one, the holes that the bed adjusting screws go down through are a fair amount larger than the screws. This will let the whole platform twist or move slightly laterally. If you don't adjust the Z shim so the springs really compress there is not a lot of tension on the bed. Also the end of the platform that holds the bed can twist quite easily.
So one remedy was to go with bigger screws which meant drilling out the bed and enlarging the counter sink to accommodate them. No thanks.
So the solution was to come up with some kind of bushing for the hole to reduce lateral movement of the bed. While doing that I decided that if I expanded it and bolted it to the bed it might stiffen it a little also.
So far it is working nicely.

It was along the idea of changing out the Z rods for larger ones. The stiffer you get the whole traveling bed the less lateral movement and less chance for layer shift. Especially on larger, heavier parts.