Hey @KingBeard.
Just to confirm so that I'm passing this along correctly, the opal glitched underground leaving you unable to collect it and then the icon disappeared from the map?
If so, out of curiosity, if you go to where that marker was, can you see the opal at all, or did it disappear when the icon disappeared?
I definitely understand the annoyance and inconvenience, but as for compensation, unfortunately, I'm not able to speculate on that. My apologies for not having a better answer for you regarding that.