The service worker skipped the system notification for any push that arrived while a window was focused, on the assumption that the page would refresh its unread counts from the postMessage. On Android the OS routinely suspends the WebAPK's renderer while its window still reports focused=true, so the message was never delivered and the push disappeared with no trace anywhere. The worker now transfers a MessagePort with the push-received message and waits up to a second for the page to acknowledge it. An answering page keeps the current behavior (no system notification, counts refresh). No answer means the window only looked focused, so the push is delivered as a normal system notification.