Cisco Nexus spanning tree issue

Have a weird situation with an N5k stack and wanted to get thoughts - particularly around Bridge Assurance - have read the docs but cannot quite work out where I am going wrong.

Have a pair of N5k switches running os 7.x (sw01 and sw02). The pair are configured with vpc and are all seemingly operational with no issues.

I am trying to hang another standalone nexus (sw03) off of sw02 as for a project I have to temporarily connect some additional devices.

I have configured a standard port channel with spanning tree type network set on both ends of the po. When I bring the link up, sw02 goes into FWD state, however SW03 goes into BKN p2p BA_inc state for all VLANs.

From researching this, it appears to suggest Bridge Assurance inconsistency. However, BA is enabled on both sides by default, and I have defined the po as type network which I understand is required for BA.

I can’t quite get my head around what could be causing this, and there doesn’t seem to be too much about BA_inc online, other than the normal suggestion that it is enabled on one side and not the other, therefore does not receive BPDU from the other switch.

All switches are running rpvst+ and configuration is largely default.

Hoping someone can offer some wisdom here, or perhaps I have missed something obvious.

Thanks