uMap points disappear after saving, closing, reopening

Two days ago I created a uMap with 4 layers (each with their own icon) and a total of about 25 points in them. The database view shows all points correctly. After saving and closing, also the preview image shows the content correctly:

However, whenever I reopen it (by clicking on its title under the preview image), all points disappear, except for 1 single point per layer (unique icon):

I tried different ways of creating new points withint these layers (e.g. cloning, or adding completely new ones), but the issue remains: only 1 single point per layer is saved (same in database view).

Weirdly enough, I embedded the uMap on my web page, where it remains correct: https://cambisol.com/projects/

How can I recover my points? And how to prevent this in future edits?

Cheers -Anton