All but one task disappeared.
I had a small list that I was doing over again every day and editing and unchecking the next day and doing it again.
While I was editing one of the items, I forget why, but I refreshed. When the refresh was done, all but the item I had been editing disappeared. I logged out, logged in with Google, all was gone but that one item.
I had forgotten my pw, I went through the lost pw cycle, logged in (in FF this time) and all but that one item is deleted. Not the end of the world, but reading all the forum messages about this has not been heartening. You say "it's impossible" but here it is happening.