Hello turingtest2. I really appreciate your replies helping me understand how all this works. Though I must admit I'm a little fuzzy on the understanding aspect. I've never had this issue before at multiple locations with many different equipment and service providers. Apple has taken a lot of time helping me trouble shoot unsuccessfully. And my ISP, through much pushing on my end, has looked into the issue stating there is nothing wrong on their end. Being clueless I even exchanged my ISPs modem to see if that would rectify the situation. It didn't.
So just to reiterate, my current configuration is ISP modem in bridge mode connected to Time Capsule (6th generation) doing the Wi-Fi with a Airport Extreme(6th generation) extending the wireless network. Again, this issue just started approximately a week ago. I am in a new location since July and things were working fine. However, there has been some changes recently. Originally I had and older Airport Extreme (shorter one I think 5th generation without 802.11ac) connected to my ISP router creating the WI-FI network and the 6th generation Airport Time Capsule extending the WI-FI. Apple had me flip the Airport Extreme with the Time Capsule so as the newer Time Capsule was directly connected to my ISP router and thus creating the WI-FI network which was then extended with the 5th Generation Airport Extreme. Apple had me do this because the Apple TV was failing to connect all the time to the network. Oddly though, the Apple TV had been working fine without issue for months before in the old configuration. Anyways, the Apple TV issue was probably related to my ISP upgrading there network in my area as I was having many down times. I noticed at this time that I was not getting the speeds I was supposed to. My ISP switched out my modem for a newer one compatible with the changes they made in my area and speeds returned to normal. Since the older 5th generation Airport Extreme was now located in the main WI-FI traffic area I decided I'd just upgrade it with the newer 6th generation model. Anyways, WI-FI is fine and speeds are good. But it seems at some point around this time is when things based on geolocation started failing. For instance I have a schedule in HomeKit to turn a light on and off based on sunrise/sunset. This obviously is now failing. Etc.
Apple had me test the HomePod and Mac by connecting to a different network, my old location which I still have access to. They both worked fine. HomePod told me the correct location, the exact address, and the Mac was able to set the TimeZone automatically.
So, basically, everyone is at a loss as to what the cause is. I think you are on to something. But it is above my head how to rectify the situation. I checked out the link you posted, https://en.wikipedia.org/wiki/Wi-Fi_positioning_system, and not sure exactly what it means. Also, not sure if I should post a screen shot for you to interpret. Is there a way to send you a screen shot privately?
IP2Location looks pretty accurate as far as I can tell.
ipinfo.io & EurekAPI shows "Not Available" for everything
DB-IP & MaxMind show two different cities close by but not exact with MaxMind showing "Not Available" for my ISP.
If you actually read all this much appreciated. It's a lot. This issue has wasted too much of my time but I'd like to get it resolved but I'm starting to give up on it. Apple tech is getting back with me Thursday to try troubleshooting some more.