So I did test this a few times as well. The only thing I had enabled (during the first test) in “System Services” was “Find My Mac”. Everything else was turned off, and the issue remained.
Just to confirm that this was a clean install of Catalina, so the only wi-fi AP in my history is my home one, as I haven’t worked in a cafe, airport, or hotel since then :-).
Since disabling Bluetooth and the system stabilizing, I’ve re-enabled “Location-Based Suggestions” and “Significant Locations” only. Everything else under “System Services” is still turned off, including “Wi-Fi Networking”.
That said, you did mention that you’ve fixed this on Big Sur. I am still running Catalina. Considering Apple’s history of dodgy initial releases of a new OS, I’ll give Big Sur a few months (or a year) before I feel it’s safe to upgrade. I’m already having to deal with Catalina as it is, which is why I have High Sierra installed on my old laptop for my weekend DJ streaming habit :-). OBS Studio seems to like High Sierra better than Catalina, hehe.
Many thanks for working on this - it’s most appreciated!