I have found a workaround for the 10-bit HEIF conversion. Lightroom allows to export images as JPEG XL which offer similar features as HEIF 10-bit.
I primarilly needed some way to convert RAW images into some format supporting HDR. And JPEG XL looks good for this purpose.
There could be several reasons why this is happening. I'm not familiar with your camera, but it probably has something to do with one or more settings on the camera that are set incorrectly.
One thing to try is to set the MODE dial to the P setting, and see if the problem still occurs. If not, then you are having a problem with some setting on the camera.
If you are using a flash, then the first exposure will be correct, but the next exposures will not because the flash has not recharged.
Do you have a user manual?