Changes

Explicitly log exception from asynchronous tasks.
Previously an UnhandledException would be thrown and the stack trace /
message would be printed to System.err in the default
UncaughtExceptionHandler for ThreadGroup. This was undesirable as it
meant that logging frameworks / exception monitors such as Sentry were
unable to get the exception. Additionally it would cause the death of
the thread in the ExecutorService. This change mimics the behaviour of
exceptions occuring during synchronous tasks.