It's a scanning failure; you've not set your black-point correctly. Red shadows in Portra are a classic symptom of using the mask colour as the black point. Have a read of the C41-scan howto in the FAQ in my signature. The gradient is usually a function of flare inside the scanner.

The subject's face is also under-exposed. With normal contrast, the face is going to be pretty dim with the background set to black. Bringing the skin tones up causes the contrast to be unnaturally high (the second scan) or the background to fail to be black (first scan). There is no cure for that other than better light.

As to agitation, C41 expects constant agitation through the whole process. Inversion should be fine, but don't do it once per minute, keep going for the whole 3:15.