1. how do you try to find the materials? prospector limpets?
2. are you looking for materials which can actually be mined out of core mining? (most hotspots mark materials which can only be core mined)
3. are you looking at the correct ring type? (painite can be core mined at metal rich, but laser mined only at metallic rings)
4. did you look at any of the many threads in "dangerous discussions" on the somewhat currently broken pulse wave scanner, in case you are trying to use it (beside it only helping with core mining)?
generally, for non-core mining materials, a hotspot raises the percentage of the hotspot material (platinum for exampel), and you should find platinum in a platinum hotspot using prospector limpets.
for core-mining materials like musgravite you won't find musgravite with prospector limpets, as you can't laser mine musgravite.