The communication seems pretty clear to me:
CG_Tophat wrote:
We had an omission from our most recent patch notes. We’ve changed when the roster lock occurs for both TW and GAC matchmaking. Previously, your roster did not have a snapshot of your collection taken until the moment matchmaking had begun. This resulted in some players rosters being updated after the moment matchmaking by the nature of the system going through and taking snapshots of everyone’s roster. Now, when you click the Join button your roster is snapped. For TW, if you exit, you are removed from matchmaking consideration. When you rejoin, your roster is snapped again at that moment. Apologies for the omission.
They talk about both TW and GAC rosters locking at Join. Since you can leave a TW, additional detail is provided to inform us what happens in that case - because you can Join multiple times. Since that isn't an option in GAC, no further description was needed.
With regards to the 36 hour GeoTB phases - there was a scheduling bug, and to compensate for that bug, they set the phases at 36 hours. Therefore the 36 hours was an intentional choice made by the developers, and was not a bug.
https://forums.galaxy-of-heroes.starwars.ea.com/discussion/207446/planned-schedule-for-grand-arena-championships-exhibition-and-geonosis-territory-battle
I know you're frustrated by this, and I also would like to see a "leave/rejoin" option or "refresh player roster" button installed. However, this forum is not the correct place for the discussion. That is the reality of the situation - and complaining about it does not change the fact.
The only bug that I see here is that when they changed the player lock at join, they didn't update the text, so the countdown "to Player Lock" is not an accurate statement and should be fixed.