I find that 3 separate anomally with that.
1. You can pack in mechanoid into vehicles and they will count as as cargo
2. On the way back, mechanoid will instead count as a separate pawn and thus the vehicle will move much slower
3. I find that mechanoid were supposed count as passenger? perhaps identical to how animals are carried in vehicles

So bascially, you need to manually pack them as pawn. On the return trip, you also need to manually pack them again but they will dismount which will makes them move much slower

I can just say that biotech is not fully supported yet. Might as well use shuttle mods