This issue became a problem for me right after I had to reinstall office on a freshly installed Windows 10 Pro. I have only started troubleshooting, this morning, but I'm guessing this has to do with "connected services" at one or more levels, locations,
etc.
The required reboot is also an indicator to review your privacy settings, as well as any changes Microsoft has made to a particular Office service's privacy policy, since the last time you opened the Office application.
With all of the possible "connected services" that exist across multiple Office components, and with the present generation of MS developers' propensity to tweak their application(s), then boot them out to us in an essentially
alpha development stage, it's no wonder this is happening on a nearly a daily basis.
I hear people saying, "but I don't have "connected services" enabled. Well, that may be true of yesterday, but each and every update (not just the announced ones) carries with it a probability that your privacy settings get changed, especially when the
updates have directly related changes to "connected services."
The only way to move "alpha-stage" services through a development cycle is to rigorously test them. For a "connected service" to get tested, it needs to be utilized, and to get it utilized requires end users to use it. That's not gonna happen in a timely
manner when a very significant number of end users have these "connected services" turned off. This is only going to get more common.
I'm making this observation based on my past application developer experience with a Fortune 500 corporation. I believe we won't hear directly from Microsoft because they're the ones surreptitiously turning our "connected services" back on. Then, when
we reboot without reading MS' updated privacy policy, we just gave them permission to leave the privacy setting as they just got reconfigured.
For me, privacy isn't so much the issue. The problem is that every software company wants at least some of my metadata, and if I approve them all, it buries almost any hope of tracing rogue, outbound firewall traffic, should I need to determine if there
is malware loose on my network.
Privacy was dead over 10 years ago . . .