Leather corals are notorious for having "bad days", sometimes weeks. I've had a Toadstool and a Thick Finger for years, and there were a few occasions that I swore they were dying or dead, all deflated and ugly looking, to the point I almost removed them. One particular time for a couple weeks, for the finger.
They've always come back, good as ever, after this period.
They go through a shedding period from time to time, called sloghing (sp?)I believe.
If your params are all in check they should be fine.
And yes, they do like a medium current. Not to the point that they are flopping over, but a nice flow.