G'day Bor7,
we had something similar to what you have. On our 3D's, the start sequence kept us guessing for a while. Whilst bringing up #2 eng, (#1 up & running). #1 would drop back to idle. We checked rigging , did PA's etc. Nothing out of the ordinary. Then we swapped AFCU's. Problem swapped , hence culprit found. (I am not sure why your snag alternates as per which one you bring up to match the 1st one up though)?
Hope this helps,
212bm.