Installing network-manager drops the network

[Ben Francis]

STR:
* Flash Ubuntu Core & accept default network settings (no Wi-Fi, DHCP on Ethernet)
* SSH into box
* $ snap install network-manager

Expected:
* Network either remains connected or is reconfigured gracefully

Actual:
* Network connection disconnected, SSH session drops, user has to hard reboot and/or find new IP address to re-connect

I'm assuming that what happens here is that network-manager takes over the network configuration, re-configures the network with new default settings, drops network interfaces and a new IP address is issued via DHCP. Is there a way this could be handled more gracefully? Does network manager need to disconnect network interfaces on installation or could this perhaps be a more interactive process?

Please feel free to move this issue if I filed it in the wrong place.

Tested on Raspberry Pi 3 & 4 with core18.