Whenever you change the NBT tag of "WanderTarget" of the Wandering Trader, it doesn't travel to the exact coordinates of the block you specify. Instead it's a little offset by 1 full block.
MC-143767
"WanderTarget" NBT tag doesn't work properly
Resolved
Invalid
0
This NBT is meant as a "get close towards these coordinates", not "get on these coordinates", if it was, it wouldn't be integers, but doubles/floats.
Also: Changing NBT during the lifetime of an entity is not supported.