Backfill timed out, client stuck at Placing

Hey, I am having a problem with FlexMatch and backfill. The whole mechanism is correctly implemented (at least I hope so) and FlexMatch works, as I can start the matchmaking on two clients and both of them get matched together on my fleet (the only fleet working right now for testing purposes). The matchmaking ruleset is also very simple for testing:

"name": "dow-matchmaking-v2",
"ruleLanguageVersion": "1.0",
"playerAttributes": [],
"teams": [
"name": "allies",
"maxPlayers": 8,
"minPlayers": 0
"name": "axis",
"maxPlayers": 8,
"minPlayers": 0
"rules": [],
"expansions": []

It was intended that a session starts up if one player is entering the search, and the rest (15 slots) are backfilled so there can be a warm-up similar to how Overwatch does it. But once client 1 is on the server and I try to start the matchmaking on client 2, it gets stuck in the Placing phase. The server logs the following:

LogGameLiftSession: Not all slots are filled, starting the backfill.
LogGameLiftServerSDK: Display: TicketID: backfill-76561198069709745-2019.03.24-15.40.51
LogGameLiftServerSDK: Display: Set GameSessionARN for StartMatchBackfillRequest: arn:aws:gamelift:us-east-1::gamesession/fleet-4c04f581-231d-4377-ade3-ec942d90918a/b01751df-43b9-4b7d-b9f0-13606ccc6b7f
LogGameLiftServerSDK: Display: Set MatchmakerARN for StartMatchBackfillRequest: arn:aws:gamelift:us-east-1:390059358320:matchmakingconfiguration/dow-matchmaker-dumb
LogGameLiftServerSDK: Display: Parsed region name: us-east-1
LogGameLiftServerSDK: Display: Adding player to StartMatchBackfillRequest: playerId = 76561198069709745, team = allies, latency = 150 ms to us-east-1
... after a minute ...
LogGameLiftServerAdapter: Display: OnUpdateGameSession called
LogGameLiftServerAdapter: Display: Backfill ticket ID: backfill-76561198069709745-2019.03.24-15.40.51
LogGameLiftServerAdapter: Display: OnUpdateGameSession reason: BACKFILL_TIMED_OUT
LogGameLiftServerAdapter: Display: Backfill was unsuccessful. Calling OnUpdateGameSessionReceived anyway to allow session to retry

Is there any mistake in my ruleset? Why can’t it backfill the match?

The fleet used: fleet-4c04f581-231d-4377-ade3-ec942d90918a on us-east-1


Thanks for reaching out. May i ask do you have a recent issue like this, since in the past weeks, we have improved our backfill feature and a ticket from March would be on the old code path. Can you try that again and let us know if any issues.

Best regards,