Oof. Sounds like something has gone seriously wrong with the database that the extension uses. Data loss always sucks and I’m sorry this happened to you. It’s not a problem we encounter often and we’re not aware of any bugs on our side that would cause this to occur.
If you keep regular backups, you could try and replace the database that ArchiveWeb.page uses to store the archived items? On my Mac this is located at:
/Users/henry/Library/Application Support/Google/Chrome/Default/IndexedDB
On Windows I think this will be:
%USERPROFILE%\AppData\Local\Google\Chrome\User Data\Default\IndexedDB
The folders we need will be prefixed with chrome-extension_oelobdeikjofjgkbgplfccjefejkjodg or similar. To find the correct string of characters (it might be different from mine as I have the developer version installed?), open the extension, go to the homepage, and look in the url bar. Mine looks like this: chrome-extension://oelobdeikjofjgkbgplfccjefejkjodg/replay/index.html
There should be two folders that we need to copy. In my case these are as follows:
chrome-extension_oelobdeikjofjgkbgplfccjefejkjodg_0.indexeddb.blob
chrome-extension_oelobdeikjofjgkbgplfccjefejkjodg_0.indexeddb.leveldb
Quit Chrome and make a copy of both folders to your Desktop just in case!
Find the corresponding folders in your backup drive that you hopefully have, replace the database folders, open Chrome again and open the extension? See if anything has returned?
I hope this is helpful and at least provides a decent starting point… If it’s a more complex data recovery issue than this, I’m not sure how much help I’ll be able to provide.
In the future, we recommend saving your files out to WACZs and keeping them elsewhere on your disk. In-browser database storage is decent but personally I have a low degree of trust in web browsers for long-term archival storage.