Hi!
Ok, then please specify where and how are you testing, because first you said you were testing it against a remote host and suddenly you said it was working in explicit mode, so it might be clear for you how are you testing but not for me, so doing a proper explanation will help to solve this faster.

Did you download the latest mitmproxy or are you using the one included in custom kali? Also remember to clear browser’s cache before trying the attack.
And if you are going to test it in the remote host first check that the arp spoofing attack is working by running arp -a and check that the router’s ip has kali’s mac address.

Greetings!
Diego