I have read that this could be a cookie related issue. I'm not clear if removing your forum cookie would fix it, or simply remove all your subscriptions. Something to try if you don't mind the risk of resetting date-related account information.
Cookies are individual client/browser based, though- my lost subscriptions are just as lost from two computers, the mobile app on my phone, and the browser in my phone.
I deleted all car-seat.org cookies from the browser I am currently using, just to try, and there is no change.
I recall, this morning, that I did get some database errors two nights ago, late- most of the site would render but there were database error messages at the top. I didn't think much of it, and it went away a minute or two later... now I wish I'd paid more attention.
Oh, well. As long as it's not a site-wide issue, it's not a big deal.