I also use the Web Client, and it stays open pinned in Chrome 24/7 as long as I have my browser open, which is typically for 12 hours at a time. I sometimes use the Android App, which syncs to my account, and thought initially that the syncing may be causing the issue, as the notes seemed to disappear when trying to sync with my phone app. My boyfriend also has access to my shared notes with him, and he logged on, and some disappeared after as well. The issue seems to only have been occurring within the past week (I can guarantee that because I use Evernote daily!), and it seems to be deleting lists that only have checkboxes. For example, I will be editing my list within the table, switch tabs or switch notes (or potentially sync on phone) and everything in that list and table will be removed completely, except for the last line that I was editing. It may be an issue where Evernote isn't saving the changes quickly enough, but how it's deleting stuff on its own is beyond me. It's as if I'm Ctrl-A, hitting delete for everything except for the last line. This has happened at least four times in the past couple of days, and it's unfortunate that restoring your history requires a paid subscription, because that seems to be the only solution at this time until the bug is fixed.