What causes TrueSync to just... stop sending messages?

I setup a series of test scenes.

Version 1) Two clients connect to a room. Press start. They load a level. Success
Version 2) Two clients connect to a room. Same as above, but TrueSync syncs some numbers. Success.
Version 3) Same as above, but using input gathered from 2 controllers to move UI elements around. Success.
Version 4) Same as above, but the clients can change between keyboard and controller locally to generate input. Success. Some difficulty getting IDs to match, but it worked.
Version 5) Same as above, but now the results of the input are used to move objects around in the scene. Hard fail!

It works just fine as long as the input only moves the UI elements around. The moment the input moves and object, the input freezes and stops updating. TrueSync reports no problems.

Wat. I was able to move UI elements around all day.