The IPQ40xx has, well, a "different" way of handling VLANs.
See, for example, IPQ40xx Switch Config "Strangeness"
I don't (yet) know the complete set of limitations, nor have I looked at the DTS for your device, but at least on the device I am working with, it seems that there is a "hard wiring" of the ports that "normal" OpenWrt-style configuration can't overcome.
Guessing, your use of VLAN 2 conflicts with the typical configuration of the VLAN used by default by the "wiring" of the WAN port to the internal drivers.