Stated getting this error the other day when launching Admin Center
Couldn't update extension catalogs. Error: The given key was not present in the dictionary.
Environment is Windows Server 2019 Core
@Paul Brock , it looks like this was fixed today (at least on my lab)
@Christian Bezençon Good to know. I gave up because I wasn't sure what was causing the issue and uninstalled WAC and re-installed it.