Given the code snippet you shared
var detailsGroup = {
id: 'details',
label: 'Details',
entries: []
};
linkProps(detailsGroup, element, translate);
eventProps(detailsGroup, element, bpmnFactory, elementRegistry, translate);
it seems like you are only adding details props for Links and other Events. The element you have selected is a connection. Therefore the details group is empty, because there were no properties found for the selected element.
For example, the LinkProps are only revealing properties, when the current element is an intermediate event. If you want to have the conditional props for connections, you will have to add it (like we do in the CamundaPropertiesProvider).