Thanks for this update - i have also had issues with decoding ambisonics.
By selecting ‘binaural’ you are telling UE to decode the ambix using the Resonance plugin. this will output fine if you are building a project for headphones or stereo, but i believe will cause issues if you want to playback using a multichannel setup (5.1 etc)
Selecting ‘Panning’ it will use Unreals native decoder which i believe works well with FOA.
Having spatialised=true will world lock the rotation, and having specialisation=false will have listener orientation.
You should be able to route the SW directly to a normal submix and pretty much leave it default settings, as long as you use ‘Panning’ - Dont use any of the specific ambisonic submixes though - it has been confirmed to me that they are not working as intended.
It looks like you have solved your issue, but i wanted to also share what i’ve discovered in case it also helped.
Good luck!