Thanks for looking into it Luke!
Checking your video I see that you are using Maya 2024 whereas I am in 2023 and 2022.
Sure enough, if I load the character in 2024: the issue is resolved.
Something must have changed relating to how Maya handles import in the current versions, I'll look into it on my end.
Unfortunately we're version locked to 2022 due to some plugins, but I can probably find a way around those now that I know where the issue is.
Thanks again for your help! I am now on the right path