Navio2 not fully working with Rover 4.3.0 and up

I’ve got my old Navio2 FC out for a new rover project. (As it’s not much use for airborne applications).
Mounted it to Raspberry Pi B+ just as I had it a few years ago and downloaded the Emlid’s specially modified OS.
After going through all the basic steps I’ve decided to upgrade to latest version for Rover. Yet to my surprise found GPS and RC receiver didn’t work.
After many hours of searching and looking through old configuration settings, I’ve decided to start fresh. (Cleared everything and re-installed OS and settings)
With the Emlid supplied Rover 4.0 everything works fine, but once upgraded to latest same result: GPS and RC input not working.
Tried a few different versions and found highest version I can go is 4.2.3.
Anything higher and the problems start.

Any ideas, thoughts?
…could it be linked to the introduction of support for SIYI’s gimbal ? (clashing)

Thanks