Flash :: Layers In A Swf Refuse To Load (occasionally, After A Cache Clear)?

I have a swf with four frames. The first frame loads an external class that acts as traffic controller - looks at the root flashvars being passed in and redirects to frame 2, 3, or 4.

Frame 2 is a basic login screen. There's 5 layers - 2 background layers, the login screen, and a dummy text field. I also have trace statements on every layer, which I have speaking with javascript and writing out to the Firebug console. Since the swf requires database access to know what to do, it only works on a server.

The issue I'm having is that, occasionally, not all the layers on frame 2 load. All the actionscript on every layer fires successfully. What I'll do is clear my cache, and roughly 1 out of every 3 times, the only layer that's loaded is the bottom layer, or the bottom two layers.

I've removed the login movie clip and replaced it with dummy text - nothing. I put a preloader on the first frame - nothing. I created a loader swf to, in turn, load this problematic swf - nothing. I thought it might have something to do with order of rendering so I made those bottom layers semi-transparent - nothing.

Does anyone have any ideas of how to further diagnose this problem? While it's intermittent, it happens often enough to demand a fix.