2 causes that I know of for burnt tips. First, LED light burn from too much LED - more in a bit... Second, too high of alk with below-NSW levels of N and P - not likely the case. In rare cases, too much direct flow or a destructive fish can do this too, but you usually see more widespread damage.
350 to 400 PAR of LED light is a LOT, so this seems reasonable. Most do not really want more than 300-350, or even less. There is a fine line that you have to walk here and you cannot take PAR readings from people with different lights since double that amount of PAR from MH or T5 seems to be no issue - this is a LED thing. I would lower them about 50-100 and see what happens. With SPS, the best way for the masses to add more PAR is to add T5 and not to turn their LEDs up.
SPS can look good for a few months whilst being unhappy the whole time, and then they can crash. You are not having a crash, but sometimes a few months of looking good can be a false positive if they are not growing quickly. If you have had a ton of new growth with appropriate colors, then that is a really good sign. The lack of growth from Oct to now is not great, but also not bad.. just seems to be stuck in neutral.
Eventually, you will need to snip that branch off and let it heal... the coral will heal from a cut faster than it will grow back over the old dead skeleton.
This has nothing to do with this, but if you get that thing a few hours of whiter light, the color will be even better. This suggestion is for WAY later after you figure this out. Daylight for color rendering and then blue-it-up for your viewing pleasure.
