Need help - ABS Delamination on flat surface

Hello again, long time no see,
I have a flat print and the top is delaminating and has holes/tears in it. (Pictures below)
The print is about 7" square with a base of a little over 1/8", Basically a flat piece with some short walls. It’s a lid to a box.
Printing flat side down on the bed and the walls face up. Using Lulzbot Black filament, Slic3r and Pronterface.
I tried upping the extruder temp from 230 to 232 but no change. Bed temp is 85. Infill is 50%.
Several test prints of this part have come out the same. The print starts out great and then as it starts to lay down the top layers it stops sticking. (Seems to be on layer 2 of the top as beneath the delamination it’s 100% solid.)
For the black ABS I use an extrusion multiplier of 0.92 as that is a good setting for the “organic” stuff I’ve printed to keep the black from laying down too much plastic.
Printer is not enclosed but I do have some 2’ x 3’ boards set up around the left side and front.
Any thoughts?
(Pictures are from a stopped print, it was almost done when I checked it and rather than waste more filament I cancelled the print.)

Wondering if the bed temp needs to be increased as maybe the large flat area is allowing the filament to cool too quickly?
Or maybe if I have to bite the bullet and build a proper enclosure?
Used up a lot of filament on this print so far…
Any help is appreciated.