Created attachment 338214 [details] simple http server to repro the issue Safari on iOS 11.3 and Safari 11.1 on OS X 10.12.6 (AppleWebKit/605.1.15) do not send HttpOnly cookies when requesting the application cache manifest or resources listed in the manifest. This breaks offline capabilities for sites that use such cookies to decide which resources to make available offline. Attached you'll find a simple python 3 program that acts as an HTTP server to repro the issue. Expected output would be requests to /manfiest and /resource with cookies. On current safari those requests are sent without cookies however.
<rdar://problem/39618631>
The issue seems to be fixed with iOS 11.4.