When I originally played through I went into another friends group who has a higher Tier and completed the invaded missions and strongholds.
When I left the group i was in World Tier 3, with my missions stating I have completed all strongholds and invaded missions.
I attempted the suggested fix, of joining another players game who was in Tier3 and completed the invaded missions and then the last available stronghold. After finiooshing the stronghold I received the message of "advancing to world Tier 4" and let the cutscene playout with tidal basin gerar score required of 425. He advanced to world Tier 4, but when I left the group and into my own instance I was still in World Tier 3.
I have relogged several times and reloaded my instance attempting to find a better server. But I can still only access world Tier 4 through another players group.
Current time and date of this happening 16/02/2019 - 5:05pm AEST.