They stay hidden for a few weeks or just days?

they'll stay hidden for quite some time. you can always try movin' them to a different part of the tank to see if they perk up. don't go move them every day, give them some time in a different location maybe and see what happens to them. they may be unhappy with some of the neighboring corals right now, who knows.

Weird - I've heard of GSP being stubborn but never like that. How big is your colony? :(

about 3 inches in diameter, nothing too huge. I moved them to a new spot, so we will see what happens

More flow, though not direct.

looks like an Alkalinity and Iodine issue to me.
water change and Ph+KH (2 in 1) buffer from Salifert should take care of it.