Mod works great until your space platforms send resources from one to another. Here's the crash:

The mod Oarc Multiplayer Spawn (2.1.25) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event oarc-mod::on_tick (ID 0)
LuaEntity API call when LuaEntity was invalid.
stack traceback:
    [C]: in function '__index'
    __oarc-mod__/lib/separate_spawns.lua:1859: in function 'CargoPodHandlerOnTick'
    __oarc-mod__/control.lua:280: in function <__oarc-mod__/control.lua:265>

We're on the latest factorio experimental 2.1.19. I saw the note that the author is not maintaining the mod anymore, but just in case someone picks it up...

Thanks for the report! Yeah someone else pinged me with a fix for this awhile back but I never got time to implement it. I'll try to push an update if I can.

Here's the proposed fix if you want to try it yourself.
(The error should point you to the source file).

for index, pod in pairs(storage.cargo_pods) do

+        -- Pods sent from one platform to another land on a platform and are destroyed there,
+        -- so they never pass through the "surface without a platform" state below. The stored
+        -- entity reference becomes invalid and any API call on it would crash the game.
+        if (not pod.valid) then
+            storage.cargo_pods[index] = nil
+
         -- Make sure the pod is now descending, which means the surface shouldn't have a platform.
-        -- This will likely break in the future if there is a way to send platform to platform.
-        if (pod.surface.platform == nil) then
+        elseif (pod.surface.platform == nil) then
             local surface = pod.surface
             local force = pod.force

Okay... I know I'm a bit late on this, but check out version 2.1.26 if you are still using the mod :)