VOIP calls problem when network changes

Hello,
we use VOIP calls functionality in riot.im mobile client (with our local matrix homeserver)
We've found strange behavior , when user changes network on his mobile device
For example:

User 1 calls User 2 (WIFI connected phone) (Audio call) -> they speak -> they close conversation
User 2 switches out of WIFI network to 3G network
User 1 calls User 2 (3G connected phone) (Audio call) -> they try to speak, but User 1 can't hear User 2.
User 2 closes riot.im app -> opens it again -> User 1 calls User 2 (3G connected phone) (Audio call) -> they speak. Everyone can hear each other
Seems like there is something like timeout at which client device updates its IP address.

No source file, test, or entry point is identified. Reproduce an audio call after User 2 switches from Wi-Fi to 3G, then verify that both participants can hear each other without closing and reopening the Riot.im app.

Written by the indexing model from the issue text.