Hi,

The author of Add-on Updater himself (I) have experienced this once, and the
workaround seems to be to visit addons.nvda-project.org website using your
preferred web browser. If NV Access server was offline, chances are that
folks would have reported problems with not only Add-on Updater, but NVDA
update checks as well, affecting folks who do ask NVDA to check for updates
every day. Since it doesn't affect everyone, chances are that the computer
(more specifically, the operating system) might be assuming that the web
trusts soon to expire security certificate without realizing that it isn't -
connecting to websites flagged as secure (such as NV Access website) would
inform Windows that the web is safer again.

Cheers,

Joseph