Two phones with identical settings (T48G and T48S)- only one connects to SIP server

[sani390]

Hey guys, another issue, but this time I can provide more information.

Maybe you've read my old thread about the (probably) bricked phone by faulty firmware update. Since I had to replace it rather quickly I ordered a new phone, this time the T48S.

I upgraded to the latest firmware, then I took a working T48G and copied all settings and imported the generated .cfg.

But then: Register failed.
After a a quick chat with the provider of our sip it emerged that the phone seems to have an issue. I double checked all settings, in the end it still wouldn't register.
Edit: Confirmed- it's no problem for multiple phones to connect to one account!

Then I fired up pcap and wireshark and noticed something interesting.

The working phone establishes a solid TCP and later TLSv1.2 session with the registration server and starts transfering application data just fine.
The non working phone tries the same but seems to send the server a "reset connection" flag for whatever reason. (I am just good with computers, but not a network professional )

I will enclose the faulty pcap. The phone is IP 192.168.178.29 and the reg. server 217.0.30.196

I would be incredibly happy if we could solve this mistery.