Hi @Threlly, @GlynH, and everyone else in this thread, thanks for your patience.

Our dev team have informed us that they use telemetry.dropbox.com as a channel to receive client side logging, error reporting, and other metrics. This is listed as a trusted domain since the primary domain itself is ‘dropbox.com’.

The Pi-Hole add-on marks ‘error reporting domains’ which is what we are gathering through that web path.
 

I hope this information helps to clarify matters.