I can confirm that I've been seeing this the past couple of days too:
W: gpgv:/var/lib/apt/lists/ppa.launchpad.net_noobslab_themes_ubuntu_dists_xenial_InRelease: The repository is insufficiently signed by key 4FA44A478284A18C1BA4A9CAD530E028F59EAE4D (weak digest)
W: gpgv:/var/lib/apt/lists/ppa.launchpad.net_teejee2008_ppa_ubuntu_dists_xenial_InRelease: The repository is insufficiently signed by key 1B32B87ABAEE357218F6B48CB5B116B72D0F61F0 (weak digest)
W: gpgv:/var/lib/apt/lists/ppa.launchpad.net_webupd8team_java_ubuntu_dists_xenial_InRelease: The repository is insufficiently signed by key 7B2C3B0889BF5709A105D03AC2518248EEA14886 (weak digest)
W: gpgv:/var/lib/apt/lists/deb.opera.com_opera-stable_dists_stable_InRelease: The repository is insufficiently signed by key 419D0ACF314E8E993F7F92E563F7D4AFF6D61D45 (weak digest)
I do know that these are just warnings, but will confuse some people.
I can confirm that I've been seeing this the past couple of days too: lib/apt/ lists/ppa. launchpad. net_noobslab_ themes_ ubuntu_ dists_xenial_ InRelease: The repository is insufficiently signed by key 4FA44A478284A18 C1BA4A9CAD530E0 28F59EAE4D (weak digest) lib/apt/ lists/ppa. launchpad. net_teejee2008_ ppa_ubuntu_ dists_xenial_ InRelease: The repository is insufficiently signed by key 1B32B87ABAEE357 218F6B48CB5B116 B72D0F61F0 (weak digest) lib/apt/ lists/ppa. launchpad. net_webupd8team _java_ubuntu_ dists_xenial_ InRelease: The repository is insufficiently signed by key 7B2C3B0889BF570 9A105D03AC25182 48EEA14886 (weak digest) lib/apt/ lists/deb. opera.com_ opera-stable_ dists_stable_ InRelease: The repository is insufficiently signed by key 419D0ACF314E8E9 93F7F92E563F7D4 AFF6D61D45 (weak digest)
W: gpgv:/var/
W: gpgv:/var/
W: gpgv:/var/
W: gpgv:/var/
I do know that these are just warnings, but will confuse some people.