Strange blue bands on images...

I tried cannonbandingreduction but it looks for horizontal bands and I don't see a setting to change it. I tried a number of flats with no avail…

Could it be rolling shutter artifacts from an LCD / Flats panel?  …Possibly if your QHY has different flat exposure time requirements than your previous camera? If it were me and I also suspected the sensor, I'd stretch the flats to check that as well. In that case the cancellation might not be happening because of a pedestal value, darks, etc..

I don't know if this is relevant, but I once had trouble with faint horizontal bands with this camera.

When I adjusted the offset they went away.

The manual says:
https://www.qhyccd.com/astronomical-camera-qhy600/

OFFSET SettingThere is no fixed “best value” for OFFSET. To set OFFSET, you should take the bias frame and dark frame at a certain GAIN value, then checkthe histogram of the frames.The histogram distribution is a peak-like curve. While changing the OFFSET value, the histogram will move left or right. We need toguarantee the range of the whole curve won’t be chopped off at the end. At the same time, we need to keep a little residue on the left side,just over 0 a bit.Pay attention that under different GAIN values, the width of this peak varies. The higher the GAIN is, the

An offset of 50 for a gain of 56 sounds good. So I’m sorry, my idea was a red herring! Sorry to waste your time.

I have had similar issues with a ZWO 533mcPro.  All came down to me capturing subs at a different offset than I had used to create a masterdark for that sub length.  In the end I created a new MasterDark with the settings the Lights, Flats and Flat-Darks used at capture.

CS Tim