I’ve been struggling with the same issue for days (my provider in XS4ALL FTTH in The Netherlands). Today I finally managed to get the router connected to the internet. Hopefully we can sort this out together 
These are the relevant settings (assuming that you are using the wan port on the router):
Editing the switch configuration is actually not needed, adding a “custom interface” (eth1.6 - for VLAN 6) as per the second screenshot is enough!
