Infill is causing problems in 3D prints quality.

[amagro 3]

Hello,

I was doing simple 3D prints (Cura 2.6.2) with a cube (15x15x15mm) and I'm getting strange results when Infill Density is used.  

The problem is an overextrussion in the corner of the cube where the Z-Seam occours.

I will put some images where we can see the same model printed with infill and without infill, the results are very diferent.

What could cause this strange problem?

Thanks

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Edit:

I found that if the Combing Mode is Off, the problem is solved, but the number of retractions increases a lot. This may lead to other problems