First off, congrats on the successful flights.

A couple of comments ...

The ailerons are very very effective on both the flash and the lightning. I dial them back a little and use lots of expo. They are very quick, but very precise.

The pitch change with flaps is to be expected. The flaps are not pitch neutral.

The pitch change with power is unusual. I would remove the nose weight, which is likely a contributing factor, and see if the problem persists. You did not mention it, but if the plane is nose heavy it probably also had a tendency to drop the nose in level turns, as well as when inverted.

Thrust line could also cause this problem, but it is pretty hard not to get the proper thrust line in this model assuming you built without modification and made sure the engine was centered in the bypass.

If you PM me with your email address, I will send you a spreadsheet with weight and balance calculations for the one I built.