The Sentinel waited, its attention entirely on the Ring. The Envoy waited, too.
For the thousand thousandth time the Ring activated. The Sentinel saw the frozen plains on the other side of the Ring and sentinel absorbed every sliver of data those few milliseconds allowed.
In the same moment, the Envoy acted. It rushed forward. Its timing was imperfect. The Ring went dark. The Envoy collapsed and remained with the Sentinel.
Only after collating and storing all of the Ring data did the Sentinel realize that something was different this time: only approximately thirty nine percent of the Envoy remained.