When opening an Office document from a SharePoint 2016 on-prem server, Office gets stuck on saving changes back to the server. Often a status of "Uploading to SharePoint" is continually shown or "Updating Workflow Status" is continually displayed at the bottom of Word. When we disabled our forward proxy settings, the behavior goes away. When we check our forward proxy logs though, no traffic appears to be blocked. In fact, our intranet is whitelisted on our forward proxy. We tried to use Fiddler to see what requests were being made, but the save process works whenever we have Fiddler decrypt the HTTPS traffic. We suspect it might be related to some kind of cert issue, but uncertain how to get enough diagnostic info from the Office client to troubleshoot further. Also, sometimes if we disable the forward proxy, open a document from SharePoint, and then save it back successfully, we can then turn the forward proxy back on and still open and save that document. However, if we wait a day, the issue returns for that document.