Would it be possible in a future version to have the Tile Assembler blend the overlap between tiles? On occasion you’ll end up with enough difference to create a line and this would be partially solved by blending.
What software are you rendering with? If you’re using 3dsmax, you can try increasing the pixel padding. This should help because Deadline will then render the pixels that the edge pixels depend on, which might help reduce or eliminate the lines.
Here’s a thread that describes a similar problem with FG maps and tiles:
viewtopic.php?f=11&t=1612&p=6981&hilit=FG+map#p6938
Cheers,
- Ryan