I was in the exact same boat. EZViz worked fine with my mechanical chime when I first installed it with the included power kit on my original 10VA transformer.
Since installing it, I've had to reset wifi a number of times (trying different options for signal strength). At some point, up to here, I noticed that the mechanical chime stopped working all together.
With Wifi sorted out, I upgraded the Transformer to 30VA and let it sit overnight. Still no chime. I tried downloading the Hikvision app on Android and don't see any option to activate mechanical chime.
I deleted the doorbell from the EZViz app and reset the doorbell. When reinstalling, if you tell the app the doorbell is already mounted, you don't get the option to activate the mechanical chime, so I reinstalled. Again.
Now my chime works.
I can only guess that a wifi reset, also resets the mechanical chime option with no EZ way of reactivating it.
Thanks for the help of the forum!