Due to a minor design flaw the top of the tank mode, Siege: War for Cybertron Skytread has difficulty staying tabbed together, and the gun doesn't tab in securely.

I identified the issue as a ledge inside the lower legs (just above the ankle) that is too tall. This, in turn, pushes the waist up, preventing the connector piece from being pushed all the way down over the tabs.

Here's a photo of where the ledges push down against the waist, with the hip piece disconnected for a clear view:




….and here a view of just the ledge by itself:




As this ledge is hidden in both modes and serves no structural purpose, it can easily be fixed by cutting it off with a hobby knife, as shown here:



Right(red) is the ledge untouched, left(green) is after slicing it off.

Do this on both sides so the connector can tab in reliably, giving a little more space for the gun and roof-flaps to plug into place.

(Just to note: This is a a miscalculation in the design. They did intentionally put the ledge there as an extra support for the waist in tank mode (it's angled to follow the shape perfectly), but they made it too tall.)