Thanks, I have success by disabling “High Performance mode”. If “High Performance mode” is not enabled, then each cart item update works as expected. Since it is Sunday and I have a lot of other tasks to do, I am happy with this quick fix for the time being.
Also, preparing a testing site takes about an hour, because of added security precautions I need to perform manually.
Maybe by sending you the logs when I am testing with “High Performance mode ON” will help you?