Polygon layer became point layer when re-opening the project

I´m making a geological map on QGIS 3.6 and yesterday I finished mapping all the lithology in a categorized polygon layer. Today I opened the same project, to continue working on it, and I found that the lithology layer had become a point layer, without any points so nothing is showing. The attribute table is fine and so are the categories.

Is there anything to be done or do I just start over? And is there a way to avoid this in the future?