First-time Clear Notification in Chat Logs Not Showing

Date & Time: ~11PM November 11, 2021 PDT
Frequency: Once?
World name: Ultros
Character name: T'lanna Svihl
Class/Level: WHM
Party or solo: Party
Area and coordinates: The Cloud Deck (Extreme)
Steps:
1. Complete trial with two players who have not cleared. Each was in a "light party" on opposite platforms.

Expected Result:
Chat log notifications would appear for all players who attained the first time clear achievement.

Actual Result:
I observed only one achievement log message which was for the person in my "light party". Three other players (one of whom did not clear before) were in the other "light party" and saw a different achievement log message for that party's "uncleared" player.

Speculation:
I doubt that there's programming for "light party" since you don't know how players will split. But it may be that since this trial is larger than most, the achievement chat log entry is proximity-based? I still would consider it a bug in the sense that if you're in an instance, achievement entries should be instance-wide.