Microsoft Teams call to PSTN drops after WAN failover

We have an issue with FortiGate SDWAN (running 7.0.10) when calling with Teams to an external number and failing over from WAN1 to WAN2. When we do a direct Teams call between Teams clients the call remains active when doing a failover from WAN1 to WAN2. But a call from a Teams client to an external number disconnects when failing over from WAN1 to WAN2.
Does anyone have the same experience? Is it maybe related to a SIP timer within Microsoft?