Assassin bug taking an age to reach final moult?

[Flammendehaar]

I have a bit of an odd one here. I have 5 Psytalla horrida currently. 4 are adults and the last to reach adulthood moulted probably a month or two ago. The remaining one is still a subadult. I got them all together and throughout their lives so far they'd always all moulted within a week or two of each other. Is it normal for one to suddenly take so much longer to moult than the others? It lay ate perhaps a week ago and it's active, always in a different spot every time I look, so it doesn't seem to be dying imminently or anything, but I lost a few others unexpectedly on the last moult so I'm anxious about it. Anyone had any experiences like this?