iPhone se gps inaccurate

I’ve run with RunKeeper for over 2years, almost daily same routes. Over the past 4 - 6 weeks gps way off - distance wrong and zig zag path. A few runs perfectly accurate, others off by almost a mile. Location also off using Maps and Google Maps. Have tried numerous “reset” instructions / suggestions.

Never repaired or disassembled. Has never been wet. I have an otterbox case. Thought possibly if there was an antenna maybe that was the problem but don’t know enough about inner workings. I’m old enough to remember testing vacuum tubes at the hardware store - at a loss with this.