If the user started to navigate away from the page, but then did not actually do so (for instance, if the application cancelled the beforeunload event, or if a nonstandard URL scheme caused the browser to launch an external app), the SDK could be left in a state where all of its HTTP requests would be made synchronously. This has been fixed so the only synchronous request the SDK makes is when it needs to flush events during a beforeunload. (Thanks, edvinerikson!)
[2.16.2] - 2020-01-27
Fixed:
beforeunloadevent, or if a nonstandard URL scheme caused the browser to launch an external app), the SDK could be left in a state where all of its HTTP requests would be made synchronously. This has been fixed so the only synchronous request the SDK makes is when it needs to flush events during abeforeunload. (Thanks, edvinerikson!)