Leather corals are strange in some ways! They can totally collapse and never recover for no reason at all! Sounds like yours has been disturbed or in the process of shedding.
Leathers when disturbed will close up for a few days unless it's going through a "shed coating" episode as it rids itself of algae growing on it. This can take 3-4 days up to a week or more before they recover.
I would place it in medium to high current and they tend not to shed as much. Trying it in several places but leave it alone for a few days before you move it again. Once the "coat" is shed, the leather coral comes back more beautiful than ever!
When they are shedding this mucus I try to siphon it out of the tank with a turkey baster as this stuff can be harmful to other corals!
Have patience and you will be rewarded with this coral!
