Explorers taking scenic route?

I've just logged into Nothisle much later than intended, so as all my explorers were sent out yesterday with an expected return time prior to the 3am reset, I was very surprised to see that about half of them were still out, with 1-6 hours search time still remaining !
This puts them roughly 12 hours behind schedule, perhaps even as much as 18 hrs late for the lucky explorers.
Oddly, it's the ones who would have been expected to finish well before the others that seem to have been delayed, if it had been the other way around I'd have assumed the server may have been down for some considerable time.
The luckies should have been due back around 5pm or so yesterday, and the 3 on short adventure searches a bit later but they're all still searching, yet the ones due back around midnight to reset time have all completed.
Must be some kind of bug because any logical explanation like an interruption to the server would have an outcome reverse to this, very bizarre.