The dropped calls issue was a bug that should now be fixed - not the expected behavior, by any means.
The echo issue could be caused by competition for bandwidth on your LAN while you are simultaneously presenting (you didn't say how you were doing this, but clearly, not via Google Voice, which has no such feature).
Overall, I do not recommend the consumer version of Google Voice for business. It has no direct customer support, and as you have just experienced, it has occasional outages or bugs.
Google now has a business-class version of Google Voice, tailored for business. It's an add-on service for G Suite customers. If you're interested, here is more information:
https://cloud.google.com/voice/