Uncaught TypeError: Cannot read property 'x-Forwarded-Proto' of undefined

When I open an error in crash reporting for our application (j9cpuk), I land on the "Summary" page. All I get is a spinning Raygun logo. Opening my dev tools shows why - the JavaScript console has a stacktrace on it which stops the page from loading further. What gives?

Uncaught TypeError: Cannot read property 'x-Forwarded-Proto' of undefined at Object.LinkedUrl (https://app.raygun.com/cassette.axd/script/40eed1cf79760f266b1c6697814d7e9c5eda17d9/Scripts/raygun:15:429751) at n.Template.ls (https://app.raygun.com/cassette.axd/script/5a441fc9137a040f1f3a72c765d13ec262dc0666/Scripts/vendor:106:6804) at n.Template.s (https://app.raygun.com/cassette.axd/script/5a441fc9137a040f1f3a72c765d13ec262dc0666/Scripts/vendor:106:5778) at https://app.raygun.com/cassette.axd/htmltemplate/ff93b4fd78071561cd3769e7a95f297aae051768/Templates:302:273 at n.Template.rs (https://app.raygun.com/cassette.axd/script/5a441fc9137a040f1f3a72c765d13ec262dc0666/Scripts/vendor:106:5610) at n.Template.JST.ErrorGroup-ErrorInstance-Tabs-Items-UrlContentView.r (https://app.raygun.com/cassette.axd/htmltemplate/ff93b4fd78071561cd3769e7a95f297aae051768/Templates:302:231) at n.Template.ri (https://app.raygun.com/cassette.axd/script/5a441fc9137a040f1f3a72c765d13ec262dc0666/Scripts/vendor:106:5427) at n.Template.render (https://app.raygun.com/cassette.axd/script/5a441fc9137a040f1f3a72c765d13ec262dc0666/Scripts/vendor:106:5379) at Object.n.Marionette.Renderer.render (https://app.raygun.com/cassette.axd/script/40eed1cf79760f266b1c6697814d7e9c5eda17d9/Scripts/raygun:1:43843) at render (https://app.raygun.com/cassette.axd/script/5a441fc9137a040f1f3a72c765d13ec262dc0666/Scripts/vendor:87:16971) at r.Region.show (https://app.raygun.com/cassette.axd/script/5a441fc9137a040f1f3a72c765d13ec262dc0666/Scripts/vendor:87:10480) at r.onShow (https://app.raygun.com/cassette.axd/script/40eed1cf79760f266b1c6697814d7e9c5eda17d9/Scripts/raygun:15:434753) at r.triggerMethod (https://app.raygun.com/cassette.axd/script/5a441fc9137a040f1f3a72c765d13ec262dc0666/Scripts/vendor:87:7226) at https://app.raygun.com/cassette.axd/script/5a441fc9137a040f1f3a72c765d13ec262dc0666/Scripts/vendor:87:18773 at Array.forEach (native) at Function.n.each.n.forEach (https://app.raygun.com/cassette.axd/script/5a441fc9137a040f1f3a72c765d13ec262dc0666/Scripts/vendor:47:5200) at i.(anonymous function) [as each] (https://app.raygun.com/cassette.axd/script/5a441fc9137a040f1f3a72c765d13ec262dc0666/Scripts/vendor:87:1869) at r.onShowCalled (https://app.raygun.com/cassette.axd/script/5a441fc9137a040f1f3a72c765d13ec262dc0666/Scripts/vendor:87:18724) at y (https://app.raygun.com/cassette.axd/script/5a441fc9137a040f1f3a72c765d13ec262dc0666/Scripts/vendor:47:21030) at r.trigger (https://app.raygun.com/cassette.axd/script/5a441fc9137a040f1f3a72c765d13ec262dc0666/Scripts/vendor:47:20398) at r.triggerMethod (https://app.raygun.com/cassette.axd/script/5a441fc9137a040f1f3a72c765d13ec262dc0666/Scripts/vendor:87:7298) at r.Region.show (https://app.raygun.com/cassette.axd/script/5a441fc9137a040f1f3a72c765d13ec262dc0666/Scripts/vendor:87:10736) at r.onRender (https://app.raygun.com/cassette.axd/script/40eed1cf79760f266b1c6697814d7e9c5eda17d9/Scripts/raygun:15:453104) at r.triggerMethod (https://app.raygun.com/cassette.axd/script/5a441fc9137a040f1f3a72c765d13ec262dc0666/Scripts/vendor:87:7226) at render (https://app.raygun.com/cassette.axd/script/5a441fc9137a040f1f3a72c765d13ec262dc0666/Scripts/vendor:87:17034) at render (https://app.raygun.com/cassette.axd/script/5a441fc9137a040f1f3a72c765d13ec262dc0666/Scripts/vendor:87:24949) at r.Region.show (https://app.raygun.com/cassette.axd/script/5a441fc9137a040f1f3a72c765d13ec262dc0666/Scripts/vendor:87:10480) at r.show (https://app.raygun.com/cassette.axd/script/40eed1cf79760f266b1c6697814d7e9c5eda17d9/Scripts/raygun:15:467737) at r.displayData (https://app.raygun.com/cassette.axd/script/40eed1cf79760f266b1c6697814d7e9c5eda17d9/Scripts/raygun:15:469785) at r.