Top layers failing/underextruding on Creality CR-10
If you decrease layer thickness, you should increase bottom and top layer amount, or set it to a fixed shell thickness. The thinner the layers the more difficult to span over the infill (there is much less filament extruded). 

You could try extra part cooling, higher percentage infill, reduced hotend temperature and slower top layer printing. But, best results are reached with more top layers and higher infill percentage.

See e.g. this answer by user "dnewman":


  That said, with very low layer heights (e.g., 0.1&nbsp;mm), there's a tendency to use very sparse infill to speed up printing time.  However, very low layer heights bridge over voids very, very poorly.  So poorly that you can have the print nearly finished only to find that the top won't close up.  Thus, don't make the infill too sparse when doing low layer heights.  MOREVER, you definitely need more top layers to get the final finished top to look acceptable.  The thin layer heights will take many more layers (many more in physical height, not just layer count) to give a nice top.  At issue (again) is how poorly low layer heights will bridge voids.  With 0.2&nbsp;mm on up, you generally get a nice, thin strand extruded which can stretch across voids. But at 0.1&nbsp;mm layer heights the printer is just doing tiny, discrete squirts of plastic which it spreads like cake icing across the lower layer.  There's not a single, fine strand extruded and instead tiny little beads.  When there's a solid layer below, these squirts have something to be spread against by the extruder nozzle.  But when there's a void, the squirts just build up on the nozzle and then come off in a big blob when the nozzle next brushes over a non-void space.