Call Failed - Mac dropping audio calls to iPhone mid-call

Hi,

I've used Continuity to place audio (cellular) calls on my iPhone via Facetime on my Mac for many years, and it's usually worked fine.

However, in the last month or so, increasing numbers of calls placed using the Mac start out fine, but then the Mac shows a 'Call failed' message. Sometimes it's after a few seconds of the call, other times it will be after around 10 minutes.

When I look at the iPhone, there is still a green phone symbol in the top left corner, which I can tap, and then alter the audio setting to continue the call there.

So the iPhone is not dropping the call. The problem appears to be the Mac, or the link between the Mac and iPhone. In all cases, there doesn't appear to have been any issue with the Wi-Fi network they're connected to.

I have searched online for others experiencing this but not found a solution.

Does anyone have any suggestions as to why I'm getting this Call Failed error, seemingly randomly?

Mac is running Catalina 10.15.2 and iPhone iOS 13.3. Both connected to same Wi-Fi network, Apple ID etc.

Thanks in advance for any pointers.