Skipping / Under extrusion

[iikkuli 1]

Hi,

For some time, my printer skips every now and then while printing. Is this normal? I've been trying my best on cleaning the nozzle with Atomic method after I switch filaments. Should I sink my nozzle to acetone? Here is a picture while printing with silver Ultimaker PLA. Tried to raise my nozzle temp from 210°C (default PLA profile) to 220. Helped a bit but still happening every once in a while. With ABS (picture with black print) I've been having sort of under extrusion I believe? Any suggestions what to do?

[iikkuli 1]

Also I can see on this silver print that it leaves a slight gap between lines when doing the flat base.