BYE is not forwarded

In PCAP it could look like this:

The reason is Local IP in the Contact header:

INVITE sip:---@143.0.*.* SIP/2.0
Via: SIP/2.0/UDP 10.77.252.155:5060;branch=z9hG4bK0cf0cdad
Max-Forwards: 70
From: "75201" <sip:75201@10.77.252.155>;tag=as4be522cb
To: <sip:51997573866@143.0.*.*>
Contact: <sip:75201@10.77.252.155:5060>
Call-ID: 29b0f9fc2055cbc86fff11c42503bb58@10.77.252.155:5060
CSeq: 102 INVITE
User-Agent: Asterisk PBX certified/11.6-cert15
Date: Tue, 19 Jan 2021 22:34:45 GMT
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY, INFO, PUBLISH
Supported: replaces, timer
Content-Type: application/sdp
Content-Length: 301

Here is the problem: Contact: <sip:75201@10.77.252.155:5060>

In this case, we see: User-Agent: Asterisk PBX certified/11.6-cert15

So we can suggest fixing externip in /etc/asterisk/sip.conf to properly set External IP on the Asterisk under NAT.

With different Switches, solution is the same, but the way to achieve it will differ.