UM2+ Seemingly random extrusion problems

[Pyrolit 0]

Hi everyone,

We've recently made the leap and bought our first 3D printer, after following the market for quite some time we decided the UM2+ was a good fit for our needs.

The first couple of prints (UM robot, 9cm² drink coaster and a figurine of Pascal from Tangled) had no issues and came out with a nice amount of detail.

Then I tried for something a bit bigger (14cm²) and prints have been failing ever since.

Before posting this I've read up quite a bit on possible causes and solutions, so far without luck.

All (attempted) prints were made using the included spool of Ultimaker Silver PLA at default settings.

I've included some relevant pictures and tried to be as complete as possible but if any more information is needed, please ask.

https://photos.app.goo.gl/mIpD81bW687n0fjy1