TAZ 6 Not sealing top layers?

My Lulzbot TAZ 6 has been having a recurring issue where the top/horizontal layers of my prints don’t seal correctly. Instead I keep seeing these thin layer lines that form a grid pattern (see attached images).

I’ve tried adjusting the Line Width from 0.5 to 1.0mm and the Top/Bottom Thickness from 0.8 to 1.5, but neither seemed to make any difference. I typically run my prints with 0.2mm Layer Height, 10-20% Infill, and a Print Speed of 80 mm/s.

Has anyone seen this type of issue before? Do you have any advise on correcting it?