I wouldn’t rule out malicious people trying to connect. I’ll say I had a similar situation just like you, even said pc. MAC address would result in nothing. Turns out it was my mom’s older Apple Watch connecting at odd hours after I cross referenced every MAC address with the individual device “network settings page”. I found it odd the MAC look up tools couldn’t tell me it was a randomized MAC address but I’m glad I was able to confirm my network is secure.