Problem with underextrusion? and how to fix it

Hi. I have a problem with configuring slicer software.

My first print started very nicely but after few minutes ~20 min the extruder pushed not enough filament and i had to stop printing and in addition i noticed one (visible) layer separation. Result: (image i attachment)

After that i started a new print but i wanted to print it out faster so i increased infill speed but it turned out that it caused much problem: [click]

How can i fix that?

Edited 1 time(s). Last edit at 06/21/2019 01:15PM by voxfuc.

I do not think this is a problem with your slicer, but rather with your hotend/extrusion hardware. Seeing the other topic you have made, I still suspect this is the hotend:
[reprap.org]

Blockages can be temporary and unclog themselves sporadically. This is the problem with these kinds of problems, they can happen intermittently and then again not show up for a print or two.

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http://www.marinusdebeer.nl/

So i finally made nice print but idk why this problem happend. Can i avoid it next time? Btw thx for reply