IMX462 (SKU B0444) long exposure issue

I am setting up a system to use this SKU for astrophotography. I successfully get it working, taking images as intended with 3-4 seconds long exposure and captured in DNG raw format using libcamera-still command.

But when I try to automate the process using a python script (which I have been using for a Pi HQ IMX477 camera for many months), then a problem appears. The scipt will ask the camera to take a number of images in sequence so that it can be processed by astrophoto softwares.

For long exposures, it is necessary to disable the AEC/AGC alogrithm in Pi to avoid a long delay where the Pi will take some sample frames to set the exposure etc for each frame. I specify the shutter speed, the gain, the awb and no preview. When I use the HQ camera, the cycle time for a 4 second capture is about 10s. However with the B0444 the cycle time goes up to almost 30s. It seems that the libcamera-still app is still taking frames for calibration. The only setting that can really override this is to specify awbgains figures. Then the cycle time fall back to about 10s. But by doing so, the camera become unstable and not every images is exposed as intended. Only 50% of the images are successful. I need to revert back to use --awb option instead of --awbgains to achieve 100% success. But then the very long cycle time comes. Is there something in the firmware that make setting awbgains become unstable in the B0444?

To provide more info on this. I tested different options for a 3s exposure, by directly using the terminal. Here is what I get:

libcamera-still --immediate --nopreview -t 50 -r --width 1920 --height 1080 --shutter 3000000 --gain 50 -o test1.jpg

The above command does not specify any white balance setting, and the images come out good consistently. Cycle time is about 18-20s.

libcamera-still --immediate --nopreview -t 50 -r --width 1920 --height 1080 --shutter 3000000 --gain 50 --awb daylight -o test2.jpg

The above command specify a daylight white balance setting. The images come out good consistently. Cyle time again is about 20s.

libcamera-still --immediate --nopreview -t 50 -r --width 1920 --height 1080 --shutter 3000000 --gain 50 --awbgains 1,1 -o test3.jpg

The above command specify a white balance gain setting for the red and blue channel. The images are wrong which is dark completely. The whole command finishs in about 2-3s.

So somehow the camera does not understand the --awbgains option, which is a standard libcamera-still option.
Any advices?

I do more tests and I am more confused.

This time I try to play around with the preview function and find that if I do not add the “–immediate” option, then the awbgains option is not creating any problem. So the best I can get now is with:

libcamera-still --nopreview -t 50 -r --width 1920 --height 1080 --shutter 3000000 --gain 50 --awbgains 1.2,1.2 -o test.jpg

The cycle time is about 15s. If I increase shutter to 4s, the cycle time is about 22s. So it seems that the overall cycle time is about 5X the desired shutter time. This is still disturbing and confusing.