Hi @marius.loots, welcome to the Grav community.
I tried to replicate your issue but can’t. I’ve downloaded Grav version 1.6.9, installed the dev-tools and created a new plugin from the command line with the command you quoted. After that went successful I installed the shortcode-core plugin and again created a plugin. Again no errors.
Do you have other plugins installed? Grav 1.6 is quite a major change so it could well be that some plugins are giving trouble. Disabling them in Admin and enabling one by one is cumbersome but is the only way to find out what causes the creation to fail.
Don’t hesitate to ask further if you need more assistance.