In Exchange 2016 when you try and access OWA or the Exchange Admin Center (EAC), you might be presented with the following error:
The webpage at https://mail.domain.local/owa might be temporarily down or it may have moved permanently to a new web address.ERR_SPDY_INADEQUATE_TRANSPORT_SECURITY
This is due to a cypher and/or hash issue and can be resolved with some third-party tools like iiscrypto. You can select the "Best Practice" option in the tool and then reboot your server.
After that, you should be able to launch OWA and the EAC again without issue.