Ok, it seems it has to do with me having the project folder mirrored on Google Drive. When testing outside Google Drive or when syncing to Google Drive is paused building works fine. I find it odd however that this only applies when using the Spine Extension (or any other extension?) and after making a change in the project. 
If anyone has a simple explanation to this I would be glad but in any case I’ll continue outside Google Drive. And start to learn about git. 