I recently switched over Exchange 2016 authentication for OWA from Forms to ADFS, this is working well for most scenarios outside of non-joined machines using Edge. When looking at the fiddler trace Edge clients will be redirect over to the adfs farm and back to exchange but instead of the mailbox loading the client has a number of 440 errors and the page fails to load. If the user refreshes the page, then OWA loads. Oddly enough ECP was also switched over to ADFS but does function for Edge.     ~Patrick