10.15.4 - Cannot answer phone calls on my Mac anymore

[Don MC]

When receiving a phone call on my iPhone, the notification turns up on my Mac as usual. But if I click the "Accept" button, the notification goes quiet for a few seconds and then says "Call failed". If I then click the "Try again" button, it calls back to the original caller.
It's as if it would try to dial the caller instead of answering them.

This came immediately after I updated to macOS 10.15.4.
Any help anyone?

 

[Don MC]

I do have the Mac connected to the same network through both Ethernet and WiFi (different IPs though). I noticed I am able to receive calls if I disconnect the Ethernet cable, but that isn't an option for me. I need both network connections. And besides, it used to work right up until the 10.15.4 update.

EDIT: If I set the service order in Network Settings to prioritise WiFi, then it works again. But I do need the faster Ethernet for my work. Something has changed with the new update.