For the past few days, every time I've started on of my Office 365 thick client apps

[Darren Kowitt]

It opens as unregistered and asks me for a product ID or a valid subscritpion userID.  I enter my userID and pw and it's fine - and has an additional animated scren about registering this computer.  But then, once I close an app, every time I reopen it, I have to go through the same hassle again.

[#2]

I encountered a similar thing several months ago. In my situation, it was Office 365 E3 IDs, AD Join, running win10 Pro, MsOffice 32 bit 2016 CTR, and the message occurred whenever running the desktop version of word/excel/etc. This started when my employee came back from a 1.5 week vacation (so there was no activity on that ID for that time period). I never got it resolved. I did a win10 refresh, getting rid of all apps and data, rebuilt the device for another worker (new profile/etc), and still was unable to run the 32 bit. I had to install the 64 bit to get around the issue.

[#3]

Is this happening for all users?

How was Office installed? Click to Run or from an MSI?

Running a Office Repair frequently fixes problems like this.