Looking at the source of the page generated by sonarr I can see that these icons exist and they do link to working icons. However they never appear under iOS.
The sizes of the icons specified by sonarr are as what appears in the following source code:
<link rel="apple-touch-icon" href="/Content/Images/touch/57.png?h=PNA6NuOLptMs7gvzj4OIpQ=="/>
<link rel="apple-touch-icon" sizes="72x72" href="/Content/Images/touch/72.png?h=EMk2eonJQ1tSTlI6vjkSZQ=="/>
<link rel="apple-touch-icon" sizes="114x114" href="/Content/Images/touch/114.png?h=+MUlWiCq1/CNfTOOL3I06Q=="/>
<link rel="apple-touch-icon" sizes="144x144" href="/Content/Images/touch/144.png?h=/H8/MlS+njb/6iYJIuMQkw=="/>
According to the apple developer site the recommended sizes are:
180 x 180 iPhone 6 Plus
120 x 120 iPhone 4, 5 & 6
152 x 152 iPad and Mini
76 x 76 iPad 2
60 x 60 Default minimum
Giving the following code snippet:
<link rel="apple-touch-icon" href="touch-icon-iphone.png">
<link rel="apple-touch-icon" sizes="76x76" href="touch-icon-ipad.png">
<link rel="apple-touch-icon" sizes="120x120" href="touch-icon-iphone-retina.png">
<link rel="apple-touch-icon" sizes="152x152" href="touch-icon-ipad-retina.png">
Safari Web Content Guide: If there is no icon that matches the recommended size for the device, the smallest icon larger than the recommended size is used. If there are no icons larger than the recommended size, the largest icon is used.
So the recommended sizes are all out by a bit but it should still pull through an icon, is there a reason for the scrambled text after the .png links to the icons?
Resources:
iOS Icon Matrix: https://developer.apple.com/library/ios/documentation/UserExperience/Conceptual/MobileHIG/IconMatrix.html
iOS Web Applications: https://developer.apple.com/library/ios/documentation/AppleApplications/Reference/SafariWebContent/ConfiguringWebApplications/ConfiguringWebApplications.html