Running KDE neon Developer Edition Unstable Branches.

KDE Plasma Version: 5.8.90
KDE Frameworks Version: 5.29.0
Qt Version: 5.7.0
Kernel Version: 4.4.0-53-generic
OS Type: 64-bit

Just ran sudo apt-get update && sudo apt-get dist-upgrade. Apt reports 272 upgraded, 4 newly installed, 2 downgraded, 0 to remove and 0 not upgraded. But it gives a warning when I reply Y to continue:

WARNING: The following packages cannot be authenticated!

And lists nearly all 272 packages. What happened to the signing key?

Update:

Hmm. So maybe I was accessing the package repositories before they were completely populated, as I just now reran sudo apt-get update and sudo apt-get dist-upgrade and apt now reports 316 upgraded, 8 newly installed, 0 to remove and 0 not upgraded and no WARNING; the dist-upgrade is processing normally.