Teams call quality

Hello

I was wondering if this behaviour has been encountered before. Last year we migrated our user base to Exchange Online. Around that time we started to get reports of Teams calls quality being poor. Now, I am not saying that this is related just the changes that have been made to our system in the past 12 months.

We've had further reports from more and more users call quality being poor. 

The main behaviour is this. Users will join a Teams meeting whether it's created by them or they are invited but after around 15 mins one or more users in the Teams Meeting will find that they sound like they are lagging similar to when a mobile phone has low or loses signal. The only way to cure it is for them to leave and join the meeting. What we've found is that it happens with a meeting of more than two people and that the users in the meeting are either at our HQ or one of sites around the county. I've made sure that the ports/destination addresses are in our Teams Firewall rule based off this link Microsoft 365 URLs and IP address ranges - Microsoft 365 Enterprise | Microsoft Learn . I have had a our networked. QoS has been enabled both in teams and on our network but it is still happening. 

I am wondering if anyone has experienced similar behaviour.

Thanks in advance.