<p>I upgraded from Cura 2.7 to 3.1.0 and I'm getting horrible under extrusion, I'm sure this is the software because I rolled back to 2.7 and everything is working fine again.</p>

<p>My printing is a Robo3D R1+ using the "custom FDM printer" profile.</p>

<p>Is there any new setting or a setting that isn't migrated properly that causes this?</p>

Some users have reported upgrades to Cura changing the filament size to the default 2.85 mm. If you are using 1.75 mm filament (which most printers do), you will get extreme under-extrusion.