The Mastodon admins say that it’s probably because of the size of my account (~600 MB), so the export process times out. And I understand that. Here on twtxt, I always use auto-expiring links when I post images or videos. It just gets too much data otherwise. I think I’ll just set my Mastodon account to auto-delete posts after ~180 days or something like that. Nobody cares about old posts anyway.