Unfortunately I can’t reliably reproduce this, but maybe it rings some bells with others. I have a cell that produces rather memory intensive output (in this case, graphics via the modules made by the holoviz team). My browser warns me that the jupyter tab is using a lot of system memory. Lesson learned: ignoring that was a bad idea.
The tab crashes, and the browser restarts a new tab with the same address. Jupyter reloads, and all seems to be OK – except that the cell I was working on has disappeared!
Has anyone else encountered this?