Why is the Grandstream 1620 configured for a cloud PBX not registering on the network through a Mikrotik router?

Question

Telephony

Tried to transfer the Grandstream 1620 phone from one office to another - it would seem, what problems could there be?
Configured for a cloud PBX Mango

When I connected the phone in the new office, I saw that the phone did not want to register the account entered into the online status. I rechecked the passwords, reset it, set it up again - it does not register (but it gives out IP to the phone).
Brought the same phone to the old office - does not register.
I got a new phone, already Grandstream 1400, set it up in my office - everything is ok. I bring it to a new office, I stick it in - it doesn’t register again (it gives out IP, you can go to the web interface), I bring it to my office - now it doesn’t go on the network from me either.

I started watching Mikrotik - he sees the phone. But the driven account on the phone does not want to go into the "online" status.

I began to suspect Mikrotik, came up with some perversion:
I connect the netbook to wi-fi in my grid with the same Mikrotik, I make a network bridge between the wi-fi and lan interface on the netbook (Windows OS), I turn on my Grandstream 1620 in the lan interface of the netbook - the phone comes out to the network, calls come in and come.

Now the question is:
Why did Mikrotik begin to be harmful to such household manipulation with IP phones.

By the way, the phones are not connected directly to Mikrotik, there are still switches between them.

How many times I transferred the phone from one office to another - there have never been such problems.

Answer 1

You have an amazing opportunity to take a traffic dump from your phone on Mikrotik PCAP and identify all the causes of the problems that occur.
I suppose that NAT translation can stick on Mikrotik: the old translation hangs and prevents the new one from working. As an option to find the old nail. Search by port (5060 or whatever you have) or by the IP address of the cloud PBX.
I had a rule: if SIP does not work normally on Mikrotik, you need to enable / disable SIP ALG on it. It helped in most cases.

Answer 2

It is not clear what it was, but in the end, turning off all switching devices helped. Those. Mikrotik and intermediate unmanaged switches.