'Do not disturb while driving' does not work properly on iPhone 8 (version 11.1.2)

"Do not disturb while driving" does not work on iPhone 8 (version 11.1.2) when set to be activated "Automatically" or "When connected to Car Bluetooth". It does work when activated manually though when activated via the Control Center. I also have a iPhone 7 as well and have tested it. The "Do not disturb while driving" works perfectly on this iPhone 7 when set to be activated "Automatically". For example, while driving if I try to access the phone, I get a option prompt saying "I am not driving" and "Cancel" on my iPhone 7. But, I do not get any such prompts on iPhone 8. I have used the same settings on both phones. I have also tried restoring iPhone 8 to factory settings and then testing it. It did not help. I have downloaded an app that tests the iPhone's hardware. There is nothing wrong with the hardware. There is no problem with the accelerometer and GPS sensors that are used to engage the "Do not disturb while driving" mode when set to automatic. Did anyone test the "Do not disturb while driving" mode on iPhone 8 and iPhone 7? Any fixes?