The 2 errors you see are expected, regarding some requests to discover services that are not active in the standard installation.
WFS protocol has the defect of respoinding 200 with an Exception in XML, so even if you have an error, it may not be shown as an error in console.
Anyway if an error occours from WFS, MapStore should intecept it, so you should see some error on screen.
If you are able to add the WFS catalog and see 0 results, probably QGIS server do not have any accessible layers published on WFS.
I'd inspect if you can the WFS request from developer tool to see the content of WFS response and check if there are some layers.
Hope it helps.