looks to me like the printer had a hard time spanning the gaps across the infill, and it never properly filled in the top.
Possible solutions:
Increase the infill percentage to get the infill to be denser and easier to span
Increase the number of top layers to give it more time to properly fill the top surface
increase the thickness of the infill extrusion
speed up the infill
add a cooling fan during the infill
If the surface is at a slight angle, increase the number of perimeters
Also if the surface is at an agle, and you don't have overhangs, select external perimeters first, so it gets better adhesion as it builds inwards
To print or, 3D print, that is the question...
SD3 printer w/too many mods, Printrbot Simple Maker Ed., FormLabs Form 1+
AnyCubic Photon, Shining 3D EinScan-S & Atlas 3D scanners...
...and too much time on my hands.