Seeing the entry Content://Cz.Mobilesoft.Appblock.Fileprovider/Cache/Blank.Html in your logs does not mean danger. It merely indicates that the AppBlock app was loading its blank HTML file, most likely to replace a web page or display a blank screen. That is what the app was created to do. It does not have any relation to viruses and malware or a threat to safety. The entry is simply how the app will conceive blocked content, hence you can confidently disregard it.