We currently use Jive-n and I have seen a massive drop in Total and Registered users. If you look at the chart below, you can see that (July 20th 2016) there was a drop of over 1000 Total and Registered users. Our Total users dropped from 3,892 to 2,408 (1,484 drop) and our registered users went from 3,582 to 2,255 (1,327 drop). The other stats - Active, participating and contributing seem about right. The smaller dip before that was accounted for by an internal error of deactivating users, which was quickly solved, and they were reactivated.
I though that it could be user decayUsers mysteriously being disabled? It may be the User Decay Task However us reading about it, it looks like it is not available on Jive-n. Even if it was, it's a task that happens every day and users would naturally start to drop off if they hadn't been logged in for 12 months, not all on the 25th Of July 2016.
Does anyone know if this is a Jive issue, or something we may have done internally?
Reviewing through your description, I see where you have also submitted this as a case in your customer group. Reviewing through the investigation there, it appears this was related to a change made by your external SSO system.