Question about bad colour negative development

[PhantomLord]

Hello,

I would like to ask you, more experience, guys about your opinions the problem I encountered.

I shot my usually day-to-day negative Fuji Superia X-TRA 400 and had it developed in lab (the same as always).
I'm scanning negative myself with Plustek 7600i scanner.

What's a bit weird is the trouble with colour balance on a few shots. Most of the negative is all right, however last 10-12 frames represents random colour cast.
All of them were shoot in the daylight, at about 6:00PM and sunlight was even, not changed by moving clouds. However when I scanned those 10 frames, 4 of them are all right and rest is showing different amounts of colour cast. Frames which are showing colour cast look as they are overexposed by 2-3 stops. Overexposed photos have, after conversion to positive, quite strong cyan cast.
My thoughts are that by overexposing by different amounts particular frames I had caused this colour casts, but I'm waiting for your opinions.
My other theory is that ColorPerfect plugin, which I'm using for negative-positive conversion, doesn't cope well with significantly overexposed frames, but this could be easily checked by trying out different software.

At the end I would ask one, ridiculous question: if something is wrong with the development, then whole negative will be messed up, right? I don't think that old or wrong chemistry could cause such differences from frame to frame, but I would like to be ensured.

I would really appreciate any thoughts or opinions on such case.

[miran]

Yes, overexposure and underexposure affect colours in different ways depending on the actual film and trying to "fix" them can quickly get painful.