Martin,
Sorry that you are seeing this issue. I assume you are working with the latest CodeMix release, CI 2020.4.7. If no, then please update via Help > Check for Updates and see if the validation error is still reported.
Is the error being reported in the HTML file?
I followed this tutorial for echarts and do not see any errors being reported for the div tag at my end. I see the reported error only if I do not add the import for NgxEchartsModule
in the app.module.ts file.
Please recheck the imports and the dependencies at your end.
If the code is right and you are still seeing the error, try re-validating the project via the Angular Control Panel (click on the Angular icon in the editor area to get the options for validation) and see if it helps. If nothing works, then please share with us the zipped project files, or the code snippets, along with the package.json contents to help us replicate the issue at our end.
Apologies for inconvenience caused.
–Swapna
Genuitec Support