Hi Brooks,
A couple of thoughts here:
1. I have used the glow powders with resin and have not had a problem with them settling out. I would suggest either using less powder or by mixing some powder with resin on a piece of wax paper, then adding this mixture to your cup of resin.
2. Are you mixing other powders with the resin? If so, I would expect there isn’t enough room for all powders to mix thoroughly. I prefer liquid colorants if I’m also using glow powders.
https://shop.resinobsession.com/collections/colorants/Liquid