Due to the outbreak of the Covid-19/Corona virus, Microsoft has added new IP addresses to its services. Within a week, Microsoft has gained 12 million new Teams users. Especially for Teams Microsoft has added a complete /14 network to handle the increased load.
They added a full /14 IP-Range (184.108.40.206/14)
Did you already made the adjustments in your Firewall?
To change your firewall to catch up with these changes please follow the guidelines on the Microsoft website: URLs and IP address ranges