You are not alone. Everyone I talk to using the latest version has the same problem.
In fact, the problem is even worse than you describe. In addition to the first few frames, any frame you happen to place the time pointer on before the render will be bright in the render. Since AE rendered the frame for the display (incorrectly) it just includes it in the final render.
I do not understand why nobody seems to be dealing with this problem. It really make ProRes unusable with AE. I have not even seen much discussion about htis particular problem on the web.
If anyone has a solution please share it. Thanks.
JT