Office Add-ins error: Cannot connect to catalog

MTSBob: We sorted this out today.

• When we were initially manually configuring "Block Web Add-ins" (DisableAllCatalogs) and "Block Office Add-ins" (DisableOMEXCatalogs), we were setting it in HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\WEF\TrustedCatalogs.
• When you configure those two settings in policy (User \ Administrative Templates \ Microsoft Office 2016 \ Security Settings \ Trusts Center \ Trusted Catalogs), it gets written to HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\WEF\TrustedCatalogs.
• Because we need to target this particular Office Add-in to a subset of users, we cannot rely on setting the Trusted Catalog Location policy items so we leveraged registry preferences in order to make use of Item Level Targeting.
  When we dropped those keys we matched our initial test configuration which was to write the Office Add-in settings to to HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\WEF\TrustedCatalogs.  Turns out that gets ignored or overridden when something is set at the HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\WEF\TrustedCatalogs level.
• Once we realized this behavior we corrected the discrepancy and decided to rely solely on registry preferences, not policies, and the add-in started working again. 

So we shot ourselves in the foot but it took us a while to realize it.