The mask/"cutout" that frames the display has been dislodged, quite likely by dropping or other rough treatment. From speaking with several others locally who use Sekonic meters in professional studio practice, "the thing has been banged or dropped" comes up as a repeating theme. Try unscrewing the four screws on the rear of the meter and pacing an investigation from there, toward the viewing eyepiece. I am unsure if the mask is internal or external to the viewing eyepiece (once the cover is removed). A professional camera repair centre would otherwise be the first port of call for worry-free repatriation if you don't want to take the risk yourself. I'd certainly take it to a repair centre so they can have a good look at everything else that might be developing.