Why Did My IP Temporarily Change From Public To Private?

Something strange happened on January 16th, 2024, and no one at Cox customer care has an explanation. I run a small online business and make affiliate commissions from about two dozen different advertisers. Every morning, I run traffic reports to see how much traffic we sent to advertisers, and to run these reports, I login to each of the advertisers' different admin websites. A few days ago, I was poking around one of my advertiser's admin sites and clicked on an option to view my login history to the site. The page comes up and shows me every one of my logins, including the date, the time, and the IP address. I scrolled back a couple pages after seeing my same IP dozens of times for the last several weeks, but then, on just one of my logins on just one day, Jan 16., the IP that was listed is NOT my IP (my Cox IP was showing up on every single other login every single day before and after Jan 16.). I know this was my login because the time stamp was in fact when I logged in, but again, the IP wasn't mine. This is the IP that showed up as being me: 242.13.205.41 So I did a lookup on that IP, and it says it's a "private" or "reserved" IP that isn't part of Cox. What's also strange is that at the time I logged into this advertiser's page, I was also logging into about 20 other advertiser's admins pages in various tabs, since I login to all of them within a couple seconds of each other when I'm doing my daily traffic reports. When checking my login history on ALL the other advertiser sites, they all show my login at that Jan. 16 date/time as my regular IP that I recognize, not the weird private one. So, this was something that happened with the one connection on the one site, and I don't know why I would've been rerouted and/or recognized as having a private IP, just by them? My worst fear is that this was some sort of hack that I encountered upon landing on this one advertiser's site, but if anyone has a less creepy theory, I'd be very appreciative. Thanks!