After speaking with a few gdevelop guardians in my original thread, it looks like the Count Object Condition is causing unintended behavior for object creation as a sub event, or as Gruk put it
this condition is interfering with the instance filtering GDevelop makes to apply the actions
Which roughly translates to "All objects of that type are being effected rather then just the spawned object. It’s as if you’re using a For Each Object loop."
Image of the event sheet can be viewed here.
Running: Windows 10, GDevelop 5.0.0 - Beta 99
Edit: Github issue created here.