My flower leather coral looked like crap for the first month after I acquired it. It shriveled up into a grayish lump and didn't do much after that for almost a year. Two months ago it started opening fully. Now it's spreading nicely to the point where I've had to cut several frags off to keep it contained. My torch, two open brains, frogspawn, pulsing xenia, zoanthids, palythoas, GSP and ricordea yuma corals all thrived immediately after they were introduced, but the leather coral was slow to establish itself. Now the only thing I can't seem to keep alive is regular mushrooms. They slowly shrink over time and eventually melt away.
Give your leather time and it'll probably be okay. I'm sure you'll eventually find one type of coral that is impossible to keep alive in your system. Try not to be too discouraged when that happens.
Good luck!