Few questions, was the slimer a maricultured piece? How long have you had it? Can you get a clearer pic of the damaged area? You said your LPS is fine, but do you have any other Sps? If so, how are they doing? I'm not familiar with the Maxspect Leds, but how high are they mounted above your tank and how long is your photoperiod? Are all the Leds at 85% intensity? Do you have access to a Hanna meter to check your actual phosphate levels? Can you double check your alk level?
As others have mentioned, I've had similar results with certain Sps.
They were usually due to one of the following: the piece was maricultured and had no chance of survival no matter what I would have done, I dropped phosphates too low and too quickly, or I stuck the Sps under LED's.. I'm lucky to have a few different tanks with different lighting systems, but I've noticed my lps do phenomenal under Leds, whereas I can't keep certain Sps at all. Moved the same Sps piece to a tank under t5 and mh, problem instantly solved. Some are more resilient to lighting changes than others...
For the bryopsis, as suggested, tech-m is a step in the right direction. Instead of just dosing it to your tank, for best results, take it one step further. Turn off your flow and use a Turkey baster to directly spray the affected area/frag with the tech-m. I've noticed a lot more effectiveness this way. Youll see it lose its blueish/greenish hue and turn more brown after a few applications. It is possible to beat it, but youll need to attack it from a few angles. (Tangs, gfo, getting rid of whatever you can that keeps growing it back, macro algae, etc). Just my .02