We have been trying to deal with this password prompt for quite a while now and for a period of time we were pointing the blame to a few add-ins. However, during today's troubleshooting I ran a status test to see what it was trying to connect to during the time of the prompt. Well I found a connection that stood out where it was trying to connect in cache mode. I decided to turn cached exchange mode off and ever since then I have not gotten a password prompt. After restarting outlook about 50 or so times I decided it was enough and tried to re-enable the cached exchange mode, and as I expected, the password prompts started coming back.
So what could be causing cached exchange mode in outlook H&B 2016 to to prompt for these windows credentials? I saw one spiceworks article where a guy was basically saying that cached mode might be connecting the public FQDN instead of the private network name and it prompts because it sees the server as being outside of the logged in domain? Just looking for a possible resolution so that we can still keep exchange mode enabled for the benefits it provides.