I try with: FULL WIPE (data, cache, system, dalvik) and reinstall on twrp the last rom 6.7.23, initial setup and test... same problem with BT ON, the wifi is slow... now I repeat with the 6.7.14... i give you feedback when try this or retry with 6.7.7 (the first miui 8 rom)... :(
PS: RR 5.7.1...