I also experience loss of changes. They seam to be triggered by highlighting one or several regions in light blue and then pressing Del or Ctrl-X. The loss is restricted to the last deliberate save using the toolbar button, regardless of how long ago this happened.
This is an example file where this happened frequently: https://en.smath.info/cloud/worksheet/N4gAxVxV
I experienced more annoying interface problems:
- Images can't be inserted repeatedly unless the sheet is reloaded using the browser refresh button. Without doing this, the user experience is that the insert picture menu item just doesn't work any more.
- The visibility of stacked regions sometimes is messed up. If you move text regions around (e.g. if you want to annotate an image with math regions) then they are sometimes behind the image (in the background) and sometimes in the foreground. This seem to be dependent on where the region originally has been created. Also, this can change if the file is reloaded or re-opened.
- Annotations (math regions with single variable names only) aren't formatted properly (italicised). You can enforce italic style by evaluating the region and subsequently deleting the result. This, however, doesn't seem to persist.
In general, these problems are hard to bracket, because of interference with browser cache. You can only be sure to see the persistent state of your worksheet if you share a link and open it in another browser instance (not just in another tab). I even switch between windows and linux running in a virtual machine.