Keep an eye on the polyps. I've had my sps lighten in color a few months ago. I was kind of amiss like you are. Then all my sps went from having great polyp extension to almost none. That's when I saw tissue erosion and lost a few frags. Once the polyps came back ,then the colors came back.

I think your lantana is adjusting to a low nutrient system. That's why it's shedding zooxanthellae and lightening in color. Just be careful with the lw nutrients. My sps always seem to go downhill when no3 gets below .2 ppm. The perfect balance for my systems seems to run between .5-2ppm no3.