The only way to find out what has happened is to get a circuit tracer and find out where the wiring goes.
https://www.amazon.com/Klein-Tools-Tone-Probe-PRO/dp/B07VYN98QV/ref=asc_df_B07VYN98QV/?gad_source=1&gclid=EAIaIQobChMIuviH8qH8hQMVx15HAR1ctAh5EAQYASABEgIdGvD_BwE&hvadid=693128046659&hvdev=c&hvdvcmdl=undefined&hvlocint=undefined&hvlocphy=9016125&hvnetw=g&hvpone=undefined&hvpos=undefined&hvptwo=undefined&hvqmt=undefined&hvrand=6694948096543929666&hvtargid=pla-830777640636&linkCode=df0&mcid=10144a5a422a31fe84f6482ac2a6e799&tag=hyprod-20&th=1
It could be a shared neutral from those two circuits. Have you opened up your panel to see if there's anything unusual going on?
The only way to find out what has happened is to get a circuit tracer and find out where the wiring goes.
https://www.amazon.com/Klein-Tools-Tone-Probe-PRO/dp/B07VYN98QV/ref=asc_df_B07VYN98QV/?gad_source=1&gclid=EAIaIQobChMIuviH8qH8hQMVx15HAR1ctAh5EAQYASABEgIdGvD_BwE&hvadid=693128046659&hvdev=c&hvdvcmdl=undefined&hvlocint=undefined&hvlocphy=9016125&hvnetw=g&hvpone=undefined&hvpos=undefined&hvptwo=undefined&hvqmt=undefined&hvrand=6694948096543929666&hvtargid=pla-830777640636&linkCode=df0&mcid=10144a5a422a31fe84f6482ac2a6e799&tag=hyprod-20&th=1
It could be a shared neutral from those two circuits. Have you opened up your panel to see if there's anything unusual going on?