If problems is only on the nss-build firmware try different ecm config parameters.
uci set ecm.@general[0].enable_bridge_filtering='0'
and restart service ecm and network.
You can also try with
uci set ecm.@general[0].disable_offloads='1'
and restart services
Verify Packet Steering is off on nns network/interfaces/global network options config.
I would like issues that affect only the nss version to be discussed in the ipq807x nss offloading thread.