Samsung S10+ and Samsung S10 mobiles both show problems when answering Nest Hello using the Nest app. There are two distinct aspects:
The issues defined above were observed when using remotely i.e. using mobile data and locally i.e. mobile on house Wifi.
A Motorola G6 was connected on house Wifi and this did not incur the same problems – no echo for the person outside of the house and acceptable audio for both users.
A Nest Hub was used to answer the Nest Hello and communicate with the person outside the house and this did not incur the same problems – no echo for the person outside of the house and good audio for both users.
The Samsung mobiles microphones have both been tested by typing *#0283# into the keypad and clicking on “SPK_2ndmic" in the Loopback Test screen – speaking into the microphone results in a very low and muffled audio playback. Interestingly, speaking into the (noise cancellation) microphone on the top of the mobile produced much better results.
Updated: Just one other point wrt VPN. There is no VPN on the router (and hence the Nest Hub) nor the Motorola G6. If I turned off the VPN on the Samsung mobiles, the audio quality does improve, but not to the same level as heard on the Nest Hub and Motorola G6 but the echo for the person outside of the house is still evident. One may suggest that the VPN is part of the problem but who doesn't use a VPN on their mobile?
The Nest Hello compatibility problem seen on Samsung S10+ and Samsung S10 mobiles is not seen when running the same test with a Motorola G6 nor a Nest Hub.
This seems to have been reported by other users since 2019 but no solution seems to be available.
When will this be fixed?
No response received so for completeness, I made one last attempt to get support, contacted Samsung via Chat.
The feedback I had was that "..that we are unable to guarantee the compatibility of this app."
So if you have Nest Hello, Samsung mobiles are not guaranteed to work with the Nest app so talking the delivery person about your delivery is probably not feasible.