iPod 4th gen, iOS 6.1.6: Apple Maps stopped working. Two iPods, affects both iPods.

iPod 4th gen, iOS 6.1.6: Apple Maps no longer works on two of two iPods. This appears to be a recent phenomenon; coincidence with upgrade on other devices to iOS 11? In iOS 6.1.6, Apple Maps has three map modes, "default," "hybrid," and "satellite." Symptom: Only "satellite" mode works, no labels. "Default" mode displays a white screen and a generic grid, no map data at all. "Hybrid" mode displays a black screen and a generic grid, no map data or satellite photos at all.