The SD-WAN rule (config service edit 1) is configured with set mode priority. This means the rule selects the best interface based on a defined performance metric, as opposed to a simple static priority or SLA. The event log (image_41cfb5.png) shows Metric latency and Message Service prioritized by performance metric will be redirected in sequence order. This indicates that the rule is using latency to determine the preferred member. Given that the log message is about a change, and the most logical reason for a change in a priority mode is that a different member is now the best performer, it implies that the latency on port2 has become lower than that on port1.
The log message Service prioritized by performance metric will be redirected in sequence order confirms that FortiGate is changing the member being used for this service. Because the mode is priority, FortiGate dynamically selects the member that currently meets the best performance criteria, which in this case is latency. The log implies a new member has been selected as the most optimal, and with the default configuration, the members are sorted based on their performance, so the outgoing interface list is effectively updated to prefer the new best- performing member (port2).