Some providers (I tried https://qms.nextgis.com/geoservices/1417/ and https://qms.nextgis.com/geoservices/797/ ) do not show on the app but they do on the preview at https://qms.nextgis.com/geoservices/...
I tried to change the zoom level and the "zoom levels to show layer" range to the maximum in the layer settings, but it does not work.