I've got av bit of a conundrum.... just started working with a new customer. I just got sent a case that Office 365 apps wouldn't start for 2 out of a few hundred concurrent users. After some investigation I find that shared computer activation is not configured on the servers. Even if I am still not sure that is the root cause in this specific, how has this not caused some major issues over the last 6 - 7 months since the site was put in to production? I will fix the shared activation configuration of course, but I can't understand why this has not been a major issue for a while for more users.

What type of environment, OS, etc?

Sorry... Win Server 2022, citrix shared desktop.

Is there a chance that SCA wasn't configured via XML, and was performed later in a GPO that may have been removed/altered?

Not sure... I'm going to try to get in touch with the consultant that implemented the site just to hear if he knows anything. My guess is that it was an oversight...

Could be wrong, but I think it is more of an issue if the profile is accessed by multiple virtual machines at the same time, so if you launch apps that hit 2 different delivery groups and are both server OS and use the same remote profile, then you get failures launching o365 apps. Educated guess by me, I saw a client had an issue where only one MC was using Office Pro Home, and that seemed to be the experience. They're upgrading to Enterprise so I haven't verified the fix yet.