@hlolli: it means you should specify asset-path. If asset path isn't correct the loader can't find all the files. Try looking in the network tab where it tries to load resources from. Likely there is something in that path that shouldn't. Then use asset-path to remove that portion.
Not a devcards issue really I think
@martinklepsch thanks for the reply. Wasnt sure if i should have taken this warning serously since i have my src and resource path set up. Nach mein Deutschkurs will ich mit asset-path mich informieren und probieren, dann im #C053K90BR weitermachen.
fixed anyway. It was as if boot would not compile new .js file for devcards, being in the same directory as the main app. So having different namespace and refer to it from :source-paths hashset fixed it. Also I could have overseen some basic error the whole time. Now time to start having fun!