If the log-on sequence of 18:25:xx was the result of a power loss and come back, was not the RAT to be extended at this time?
Not necessarily. Three things will cause the RAT to deploy automatically:
1. Loss of AC power to both AC transfer busses in-flight.
2. Both engines failed and centre system hydraulic pressure low.
3. All three hydraulic system pressures are low.
Given that the aircraft flew on for a number of hours after the log-on attempt at 1825, it seems unlikely that any of the above events occurred at that time.
As Propduffer said above, the log-on at 1825 could have been caused by a power interruption to the satcom system. Possibilities include the tripping and resetting of the satcom circuit breakers, or some other short-term interruption of power to the AC bus that supplies the satellite data unit.