This is an on going problem I have had for several years and I am once again trying to figure it out, my first post on this problem was on 8/10/2014. The problem I am having is that eventually I end up with an 1/8th inch gap between the board and the left side of the squaring plate.
The board is perfectly square and flat (I have the same problem when I use the Universal Carrier Board) as was discussed in my post from 2014 I have checked the following:

head pressure - 85lbs,
the head is level within .001 on a 14" wide board (which I think is good?)
checked the bolts for tightness on the vertical posts
the out feed tables are adjusted properly
I took the belts off and made sure there was no sawdust build up in the springs

I have now discovered that the board stays in contact with the squaring plate as the machine runs the board all the way to the left during the measuring process but when the board starts moving back to the right as soon as it contacts the right pressure roller the board will shift a little away from the squaring plate on the lefthand side then as the board travels it's length again I end up with the gap on the left end of the squaring plate and the right end still in contact. Does anyone have any suggestion?