Weird pattern on the top of a print, never seen this before

The jobs before/after this were fine. I have hundreds of prints and about 10 on this new roll of PLA w/o this occurring. The ONLY different on this one is that it's the longest print I've printed in a while (10 hours). It's 20% infill and I think the pattern is the infill pattern but not entirely sure. Anyone ever seen this? It's more of a cosmetic issue than a structural one but I'd like to nip any problems in the bud when possible. After some research I think it's called pillowing. I have a custom printed nozzle shroud and a cage fan fan which doesn't seem to be moving much air. In all fairness I don't recall how much air it moved before however. It is spinning however. Also looking a bit deeper it seems I also may have reduced my layers to .14mm from my normal .22 which may have done it due to the thinner top layers although looking at cura settings in repetier it shows top/bottom layers should always be .84mm so I don't think that the layer thickness is changing the top layer thickness.
Thank
Dave

yeah the top number of layers is low, and the top skin is too thin.

So the plastic is falling into the infill.

More top layers should fix it.

Thanks much, sort of what I assumed. What do you guys normally run for top layers? If I have top layer set to.84mm, wouldn't the top layer be .84 regardless of layer height? I've been running the .84mm top layer setting for years w/o any issue.Dave

depends on the slicer. but generally that should not change - unless you've changed the infill which would effect the size of the gaps that need to be bridged.

Might just be a change in the filament formula that means it needs a lower printing temp.

Unfotunately this is why 3dprinting is still more of an art than a science :-)