Error 8015190A on both Series X and 360, Can't Download Profile.

Recently, I acquired an Xbox Series X and an Xbox 360E and I have been enjoying playing Xbox 360 games on both consoles for a few months. Yesterday, my fiancé got me a hard drive for the 360, so we could play some original Xbox games and also download some of the games I purchased digitally. When we installed the hard drive, we queued up a bunch of games to download, and also inserted an original Xbox disc. This particular disc happened to be an unsupported game (MechAssault), but we wanted to confirm it doesn't work and get that out of the way before we moved on to a game that we knew would work (Lego Star Wars: The Video Game).

Anyway, as soon as the prompt came up telling us that MechAssault wasn't supported, my profile was disconnected from Xbox Live, and when I tried to reconnect, I received the error message saying "your console can't connect to Xbox Live" (8015190A). After running the network connection test and retrying a few times, I tried signing in on the Xbox Series X (with the 360 dashboard while running a 360 game) and I received the same message. My normal account on the Series X works just fine, but my 360 profile no longer works on either console.
I tried just about every recommended action that I have seen in the forums, including deleting my profile from both 360 and Series X, clearing system cache, cloud storage cache and content cache, clearing local Xbox 360 storage on Series X, toggling on and off 2-step authentication, changing password, etc. I have also, of course, restarted the consoles many times throughout troubleshooting. I still cannot redownload my Xbox 360 profile on either console and I still get the same error message for both.
The only recommended solution I haven't been able to try is toggling on and off reoccurring billing, because that option is not available on my account, probably because my 2 year membership of Game Pass Ultimate was included with my Xbox Series X, purchased from Verizon. When I go to the "services & subscriptions" tab on account.microsoft.com, "Xbox Game Pass Ultimate Purchased from Verizon" shows up, but it doesn't show anything about end dates, renew dates, or reoccurring billing, and when I click "manage," it takes me to a page that doesn't show Game Pass at all. If I go to subscriptions on my Series X console, it does display my Game Pass Ultimate membership as "active," and if I try to "join" Game Pass again on the website, it prompts me that it would conflict with my current subscription.
Other profiles on my 360 and Series X are still able to connect to Xbox Live, but my profile can't even be downloaded to either console, let alone connect to Xbox Live.
This is very frustrating, as I primarily play Xbox 360 titles, mainly online multiplayer with Xbox Live, which I'm locked in for 2 years paying for with "All Access," and I can't access it anymore.

Can anyone help?

:)