On my new s5 i’m having underextrusion issues in top/bottom layers and it seems to be random and/or model dependent... Small prints usually do not have this issue but anything bigger is usually underextruded at some point.   I’ve seen it happen in bottom layers even at the early beginning in layer 2 or even layer 3 (after layer 2 was printed without issues...) It happens in top or bottom layers and sometimes it’s underextruding a whole full layer and the next one is fine again.