I think two things turned this plant around. The first thing was transplanting it into coconut husk chips which is my now go to Hoya potting substrate. I got it into a routine of dipping the entire pot into a nutrient solution once per week. The second thing was getting these flat mites under control with a spraying of sulfur. Finally I had a healthy plant that rather than struggling to get it to grow, I now struggle to keep the growth in check.