When building the stock external command seat, the resulting Vessel object is created with type='Rover'.
I was able to make it 'pickable' by editing the save-file and changing it to 'Dropped Part' but according to another user, changing it in game to another type of craft also solves the problem
Please give more details on how you created the command seat, and how you tried to pick it up (I assume stock inventory, but confirmation would be good). As for creating: pad? survey site?
When building the stock external command seat, the resulting Vessel object is created with type='Rover'. I was able to make it 'pickable' by editing the save-file and changing it to 'Dropped Part' but according to another user, changing it in game to another type of craft also solves the problem