Audio delay on inbound calls only

Hello guys. I noticed this a while back with my system, but haven’t had a chance to address it until now. If I call my Yealink SIP phone from my cell phone, and I say a one syllable word, it might take upto a half second before I hear it in the handset. If I call out from the handset, the delay is much smaller. What would cause this? How do I diagnose?

FreePBX 16.0.40.4
Yealink hard phone
PBX is local server behind NAT
Internet is fast
SIP provider is Flowroute

Which Yealink model are you using? I had the same problem that incoming audio had a slightly higher delay on our Yealink T33G models than on other phones.
To make things sure that is has nothing to do with our pbx I have tested calls directly over the IP address between a Yealink phone and MicroSIP. There was still a higher delay on the Yealink phone on the receiving end.
I have played with the jitter buffer settings on the phone itself which helped a little bit but wasn’t perfect.
I have also posted the problem on reddit and the official yealink forum but got no luck there.
So long story short, I have opened a ticket with Yealink and to my surprise they gave me a new firmware which fixes the problem completely. This firmware version is still not available on the official support page of the T33G model. This was one month ago.

Reddit post: Reddit - Dive into anything
Yealink forum: Audio Delay - Disable Jitter Buffer?

I have two models, a T23G and a T42S. They both do it, which is why I was wondering if it was the PBX.

Did you also test it on internal calls?
You can enable IP Direct Call on Yealink phones and just call the phone by its IP address. So you have no pbx in-between.
Also try to set the jitter buffer to fixed and set the min/max delay to zero. Maybe this helps.

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