I just updated my iPhone XS to IOS13.4 and realised when I called someone via FaceTime through wifi, it would connect 4G after being connected (home wifi, no signal issue). It has never happened to me before. I have googled it and some people had this issue back to 2015 up to now. I wonder if there is a way to fix it? or is it iOS bug reoccurring?
Thank you very much.