Am I right to assume your talking about a widget in the hud of your game? (and not as a billboard in the game world), If that is the case tracing cant hit the hud elements - and not knowing more I cant be sure why your trace would fail.
If I was to guess maybe the trace hit the turret mesh, (that Im assuming is suspended under the cursor), and not the ground plane as intended, whatever the case Id recommend using a print string node and feeding in the name of the hit actor to debug that.
Post more info if you could use more help.