VGA needs HSYNC and VSYNC separately, so we need
Amy - VGA
11 - 13 hsync
12 - 14 vsync
A genlock connects to pins 1&2, we don't need it, so nothing should be there at all.
Any electronics inside the adaptor? Then don't try this!
At first I'd try opening the hsync connection before powerup and connect it afterwards. If that doesn't help, try the vsync. After that try closing the line with a ~100 Ohms resistor and see if Amy boots. If that doesn't work, try a larger/smaller one, depending on whether the pic doesn't sync (smaller) or the problem does not go away (larger). You might have to try as high as 10 kOhms or as low as 20 Ohms - as long as you don't short anything, nothing can break.
(What this does is to add an additional, serial resistor to the signal to limit the current and thus limit the voltage drop of the signal on the Amiga side - a rather case specific solution that produces a very special kind of adaptor that might not work in other situations.)
If all this doesn't work (sync is lost, but problem stays), you'd need to add a 74LS14 or similar to amplify the sync signal (also present in C= adapters) - this is the much cleaner solution (mil spec ;-)), but it's much more work.
