Unity iOS Crash when starting recorder

Hi,
My App crashes about 25% of the time when joining a room and starting a recording (instantiating a prefab containing a PhotonVoiceView component). If I don't start the recording everything is fine.

Xcode shows the crash in AudioIn.mm in function performRender, line 131:

cd.pushCallback(cd.pushHostID, (float*)data.bytes, (int)data.length/sizeof(float));

Using PUN2 (2.17) and Voice2 (2.13), Unity 2019.2.21f1

Any help appreciated, it's awesome when it works, would love to be able to enable voice!
Thanks