When I place down a thrower inserter on a space platform, something weird happens. Instead of throwing it into the void of space, the inserter hand stretches out like mr fantastic and deposits the item 15 tiles away. That wouldn't normally be much of an issue except the whole thing takes like 5 whole seconds and then takes another 5 seconds to retract back to pick up another thing and the overall throughput tanks as a result. For some reason, it works as intended if I go into a sandbox world and place it down directly via godmode, but apparently the space platform building process just completely breaks it. Also, whenever I try to adjust the range of a thrower inserter on a space platform, the game crashes.
The mod Renai Transportation (2.0.16) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event RenaiTransportation::RTInteract (ID 201)
RenaiTransportation/script/event/interact.lua:72: attempt to index field '?' (a nil value)
stack traceback:
RenaiTransportation/script/event/interact.lua:72: in function <RenaiTransportation/script/event/interact.lua:3>

Edit: I downloaded the mod in the middle of my playthrough, but when I tested it in a fresh sandbox world, it still happened (placed via mapview like in a normal game).

so it turns out that the way things are built by the space platform is not the same as the way things are built by the player, even though the player is still the one placing things down on the platform. I assumed they did, and I did all my testing in the editor so they worked properly like you described. Now that I know that I should be able to fix that pretty easily (probably). Thanks for letting me know 😎

Also: factorissimo 3 uses the same animations as space platforms when building materials are provided via construction bots. I have no idea if it's the same mechanic or not on the back end, but either way it still works as normal when placed there. Again, I don't know what's happening on the back end, so I can't be sure if it's a mechanical difference or just the fact that there's gravity but you can never have too many data points.