Umap data missing - is there a way to get it back?

[Floppy_Drive]

Hi, I am a newbe at Umap. I added some lines in a Berlin map. I did this a few times on different days and so far, saving the data worked well. Today however I opened the map and there are no lines left. Is there a way to get the data back? I am not aware that I did anything different the last time I added lines, which was yesterday. The link is:
Berlin - uMap.
Thank you very much for your support!

[Floppy_Drive]

This is where I started. Then I clicked on “bearbeiten” (edit) and then it looks like this:

[Floppy_Drive]

Here I started to draw lines. This data was saved a few times, but now all lines are gone.

Thanks again for your support!