Removing Authentication doesn't seem to work

TLDR: Opened “Software and Updates” to the “Authentication” tab, highlighted (I think) non-critical entries for ungoogled_chromium and iridium, clicked “Remove,” entered my password, but nothing happened.

Verbose Output: Hi everyone. First post, hope it’s fittingly n00btacular. I’m running the latest, fully updated PureOS on a Librem device for about a year now and have been really enjoying it. Thanks to all who work on these projects and keep them going!

I have successfully installed some applications from the official repos as well as .deb packages directly from some other sources. Somewhere along the way, I granted software update authentication to some of those other sources, and I’d now like to revoke it.

I’ve only tried this via the “Authentication” tab in the “Software & Updates” GUI but am open to solutions using the command line.

Most of the entries in the list end in debian.org or puri.sm, of course.
The entries in question I’d like to remove end with:

<home\x3aungoogle_chromium@build.opensuse.org>
iridium-release@iridiumbrowser.de

When I highlight one of the above and click “Remove” and enter my password, nothing happens. I did install or attempt to install each of the above but have since removed them (fully, I think, with apt-get remove and apt-get --purge).

Are these two part of the default list of authenticated software providers? Where can I find a list of the default Trusted software providers? Searching the forums and web hasn’t produced any helpful results.

I’m a little hesitant to simply click “Restore Defaults” just yet.

Other relevant(?) details regarding what I see in the “Software & Updates” panel:
PureOS Software tab has “Officially Supported” checked (from Main server)
Other Software tab shows only amber-security and amber-updates, both checked

Thanks for any advice you could provide…