EDTA becomes increasingly less soluble at low pH (and vice versa); GLDA’s solubility is less pH sensitive. However, you use it at a low concentration and the main issue you’ll see is the slow speed at which they dissolve (you’re unlikely hitting solubility limits). To speed up dissolution, use a smaller amount of water with a higher pH to make a concentrated stock solution. Some shampoo ingredients come at high pH, maybe use these to dissolve the chelates (especially if you make products for your personal use) 😉 .
BTW EDTA is often more effective (stronger binding at lower pH) whilst GLDA is better for nature in several regards.