I'd like to know what your water parameters are (I'm sure I'm not the only one). Have you changed out bulbs recently? Any changes in other critters, or just the leathers? A bit of history would be helpful, as well.
Leathers are odd that way- you are never quite sure if they are responding to external parameters or their own internal rythms. I would say just double check your water quality and maybe put them in an area of slightly increased flow.
That being the case, if you've got lighting that is significantly different from what they've been under, that may be the issue for them. If so, and you haven't already, I'd suggest placing them in the lowest, dimmest (ha!) reaches of the tank, then slowly acclimating them to the light by moving them upwards.