When issuing a "sudo apt-get update" after upgrading to "Stretch" I receive the following messages, eleven in all:
The hardware is a Pi 3 running as an always-on media server via Ethernet: wireless is disabled. The SD card shows 17GB free (using "df h").
It was necessary to "sudo apt autoremove". That said, Sonarr, SABnzbd & Plex updated correctly.
Everything else (including access to the Internet) appears to be working correctly.
NB: I have similar issues after upgrading a Pi 2B.
Any assistance greatly appreciated.