It’s a wild variation that nobody can explain and is unique for everyone.
I have a lps dominant reef and I have many Goni and sometimes they just get moody. I’ve had ones just stop opening and die. I’ve had ones that grow slow. Others Open daily but haven’t grown for months. Some have had significant growth. One has spent weeks not opening at all then randomly started again. Another (my first, a maricultured) has been open every day even when others are upset. I have some that extended 3” since arrival date and after 3-4 months, they only now extend 1” and I don’t know why
Pretty much, they do their own thing, and your tank conditions - lighting, flow, trace elements, nutrient levels have a huge impact. It could do fine at the store but hate your tank. There are tips people have on how to be successful with them but the reality is nobody knows for sure.