I created two collections over the last week or so, and I was able to come back to them several times and modify them – adding/removing references to add-ons, changing my comments associated with the collection and with the add-ons – but last night, when I tried to find them, they were gone. When I log into addons.mozilla.org now, the site says: “You do not have any collections.” They are still missing this morning. I could probably recreate them, but I don’t want to bother if they are going to disappear again. Does anyone have any ideas about what might have happened to them?
Are you sure you’re going to the same account? Maybe you created two accounts? If not, do you have a link to your account page?