Does Xiaomi K20 pro support 4G B5/B7 band and VoLTE?

[soriyari]

I bought K20 pro today and I have put a sim card which VoLTE B5/B7 band. It took awhile (might be 1mn to 1.5mn) until signal show up with 4G symbol above it. After around 15s later, signal drop and 4G symbol disappear like no sim is insert. I am not sure what is going on but seem like it is not support this sim. Does anyone has any ideas?