CF-E313ac 802.11s mesh transparent bridge issues

I have a pair of CF-E313ac's which are 5GHz devices with 12dBi antennas designed for PtP/PtMP. I am on OpenWrt master and I have them running with 802.11s mesh, which is all working nicely except that I would like to see speeds closer to the ethernet interface maximum of 100Mbps, right now I only get about half that.

I have them plugged in to a 120Mbps LTE router (confirmed getting that speed when plugged directly in) but my throughput across the two E313s using is only around 50Mbps down. iwinfo shows the link wifi speed as about 650Mbps, so what is happening?

I am using wpa3 encryption on the mesh wireless, could that be the speed goblin?

What are some general tips and best practices to optimise this kind of setup for speed?

OpenWrt ToH entry

Update: moving them further apart (about 6m apart) has increased the speed to around 75Mbps, I think it was just antenna alignment or self interference.

But now I'm getting a new problem - the eth1 WAN iface on the side connected to the router goes down after about 15 minutes of downloading a 6GB file transfer (80%). Unsure how to continue diagnosing this. Sometimes it comes back up but only at 10Mbps half duplex. Could it be faulty PoE adaptor, cable, or would it be more on the driver side or PCBA hardware side?