VLAN throughput issue

I'm having an issue where traffic that is VLAN tagged to anything but ID 1 struggles to pass more than 20mbps but only in one direction.

The setup is bridged throughout as follows:
MIkrotik Core Router
Nanobeam AC
Nanobeam AC
MIkrotik RB450 (all ports single switch)
Power beam 5AC - 300 ISO
Power beam 5AC - 500
ER-X-SFP (all ports assigned to switch0)
Rocket AC Lite
Nanobeam AC/Litebeam AC

If I run a speed test without using any VLAN tagging then I get 100mbps+ for both download and upload. However if I create a VLAN tag and assign LAN port to it on the Nanobeam/Litebeam then I can only get around 20mbps download but still around 50mbps upload. It's also the same if I use VLAN tagging on my laptop interface instead of on the Nanobeam/ Litebeam.

I have tested the throughput of the VLAN at the RB450 and it is as expected and i also have a LBE sector connected to the RB450 with a LBE client and that works perfectly with VLAN tagging so by process of elimination it looks like it's the ER-X-SFP that's causing the problem. It's running 1.8.0 but it also does it on 1.6.7.

What am I missing?