lockInbound acquired the global registry mutex and then blocked on the
per-inbound mutex without releasing the registry first. A slow client
operation holding one inbound's mutex (for example a bulk delete pushing to
an unreachable node) made the next waiter park on that inbound while still
holding the registry mutex, which in turn blocked lockInbound for every
other inbound — freezing client mutations panel-wide. Release the registry
mutex before taking the per-inbound lock.
MHSanaei