I think I found a clue… when I build the MonoGame project, it calls MGCB.exe (don’t know where though, it’s not in build actions), and it calls it with an absolute path to the directory of the project, and MGCB.exe looks at the wrong place, for example, this:
“C:\Program Files (x86)\MSBuild\MonoGame\v3.0\Tools\MGCB.exe” /@:“G:\TESTS\uimg\GeonBit.UI-master\GeonBit.UI.MG36\Content\Content.mgcb” /platform:DesktopGL /outputDir:“G:\TESTS\uimg\GeonBit.UI-master\GeonBit.UI.MG36\Content\bin\DesktopGL” /intermediateDir:“G:\TESTS\uimg\GeonBit.UI-master\GeonBit.UI.MG36\Content\obj\DesktopGL” /quiet
still looks at the working directory, I don’t know if it’s a bug in MGCB or what, but that returns with error code 214 and when ran in cmd it says it can’t find the resources.
This pipeline thing is driving me crazy though… it shouldn’t be so complicated. A lot of things seem to work by black magic so when they break you have no clue on how to even start to fix it.
Also, the MG36 project isn’t 100% correctly configured, the DataTypes is still linked to 3.5 libs.
I’m finding these error messages much more cryptic than C++ 
hehe.