I've encountered a problem with the Categorized renderer in QGIS. I have a GeoPackage file including a set of data points, with approximately 30 attributes (mainly strings). I'm trying to set the colour of points depending on a string attribute value, using Categorized renderer.
When I click on the "Classify" button, the values of the relevant attibute are not loaded and the classification won't succeed: there's only one symbol/colour for all points. The values can't be loaded in the Field Calculator, too: upon clicking the "Unique" or "Sample" button the field beneath stays empty. The Attribute Table on the other hand is displayed correctly, with all values for all attributes in the right cells.
This occurs both in QGIS 2.18 and in QGIS 3.2, in the case of this specific file only. Also, some of the attributes are not affected. The problem can be bypassed by saving the file as Shapefile instead of GeoPackage, however then the attribute labels (Headings in Attribute Table) are cut short, so such approach is not practical.
Could someone help me understand what is going on and how to make it work?
I suppose it may be a text coding issue, but I can't change the coding method for GeoPackage format (the field is greyed out).
The GeoPackage file can be downloaded from here: https://drive.google.com/file/d/1-GUObpa4yanmX9Y1tBIPAmsh1kgQB9NL/view?usp=sharing
The file contains a list of creches in Olsztyn, Poland, with addresses geocoded using MMQGIS/Google Maps (publicly accessible data only). I've only been able to use the Categorized renderer with the attribute "Telefon" (phone number), but not with other atributes.