Help please, banding in image appeared after meridian flip

[AndrewRrrrrr]

Hi All,

Looking for some ideas/help as to what might have gone on here please.....

Set up for M33 a couple of nights ago. Took approx 100x 3min subs with a flip in the middle.

When I put all the lights into APP, I got a very unsatisfactory stacked picture (never had this before), loads of banding.

I've never had to separately stack the 2 sets of lights before but on a hunch tried stacking the pre and post flip sets of lights separately.

The stacked picture on the pre-flip lights is fine but the post-flip one is weird. Have attached the two stacks. 

The camera is modded Canon 40D. Flats, bias. No darks, but dithered. 

I used the same master flat, master bias and bad pixel map for both stacks. 

Haven't done processing in particular with the 2 pictures.

I seemingly have developed a dodgy usb connection to the camera and it did unplug/plug itself quite a few times during the flip, and I had to reset things to carry on with the imaging run.

Am aware of the good ol canon banding thing, but a bit weird appearing like this. Maybe the camera went on the fritz after being connected/reconnected multiple times. If thats the case, I hope it's a temporary thing!

thanks in advance for any comments

Andrew