How to fix FaceTime using LTE instead of Wi-Fi only?

According to the report, this error appeared from iOS 12.4, but until now Apple has not fixed it. It is annoying for users to automatically lose a Wi-Fi connection and switch to a mobile data network while making FaceTime calls.

Instead of turning off LTE mobile data network for iOS devices, you can apply just disable mobile data for FaceTime. FaceTime is then required to use a Wi-Fi network without consuming your mobile data.

• To do this go to Settings (Settings)> Cellular, then scroll through the list of applications to the FaceTime stream and turn it off.

• And you only need to turn this option on when there is no longer a Wi-Fi connection and want to use LTE network for FaceTime.

Apple has yet to release an official fix or patch for this strange bug. Hopefully the company can perform bug fixes on the upcoming iOS 13.6 or iOS 14.