Unable to find subscriptions on Apple Account

The threads that appear are usually those you originated.

If you click on "Participation" says:

Total number of threads replied to 25

So, you may have participated in threads others began?

Those threads would appear in their profiles.

You can click on "Search" at the top of discussion pages to search the community.

If you kept the email notifications of posts you subscribed to by participating, they would have details and links.

The Photos - Apple Community website can be filtered and searched to find threads.

Good to know you tracked down that missing thread! Thank you for letting us know.

Tips: See your content at a glance in the Apple Support Community - Apple Support

Re:" I'm just puzzled that the questions I asked then, as well as earlier ones, don't seem to be available under my account anymore".

Sorry I don't why. You may want to reach out for an answer from those in charge:

You can: email communityaccounts@apple.com

I believe older posts just get removed after a while. Not deleted, but just removed from My Subscriptions.

There’s a way to try and search for your old posts using a browser, but I do not know how, exactly. If someone could send Allen Jones here, I think he knows how to do it. Thank you!

Seems there is only this one (listed as "recent activity" ) at armtmurp’s Subscriptions - Apple Community