Hi,
Check your nitrates and ....how old are the bulbs in your light? Xenia likes a little nitrates...too good of conditions cause them problems, as well as too high (over 20). Xenia also needs good lighting, and if the bulbs are old it affects them as well. The good news is, if the lights are so old it melts into a pool of snot...as soon as you replace the bulbs, the pool of snot will sprout new Xenia...so don't clean anything left of the coral if it melts and seems to die. Hardy stuff xenia is.
If the coral is just kind of closed up and not melting...it may be feeding, the pulsing flower tops act like little hands grabbing food, and they make a little fist if they get some yummy stuff. From the pictures it just looks unhappy...maybe something is nipping algae around it, or crawling over and irritating them.