Complement `TestThreadReceiptsInSyncMSC4102` flakes w/ `ephemeral.events` not found

[gamesguru]

Description

Triggered occasionally during Complement (workers, Postgres) runs. Also observed in Rust servers, so I'm unclear whether this is a Complement or homeserver issue.

https://github.com/gamesguru/synapse/actions/runs/28659228230/job/84995894180

❌ TestThreadReceiptsInSyncMSC4102 (7.17s)
      client.go:860: [CSAPI] POST hs1/_matrix/client/v3/register => 200 OK (36.835838ms)
      client.go:860: [CSAPI] GET hs1/_matrix/client/v3/pushrules/global/postcontent/.io.element.msc4306.rule.subscribed_thread => 200 OK (3.879651ms)
      client.go:860: [CSAPI] PUT hs1/_matrix/client/v3/pushrules/global/postcontent/.io.element.msc4306.rule.subscribed_thread/enabled => 200 OK (5.755584ms)
      client.go:860: [CSAPI] GET hs1/_matrix/client/v3/pushrules/global/postcontent/.io.element.msc4306.rule.unsubscribed_thread => 200 OK (2.220003ms)
      client.go:860: [CSAPI] PUT hs1/_matrix/client/v3/pushrules/global/postcontent/.io.element.msc4306.rule.unsubscribed_thread/enabled => 200 OK (4.436598ms)
      client.go:860: [CSAPI] POST hs2/_matrix/client/v3/register => 200 OK (33.932281ms)
      client.go:860: [CSAPI] GET hs2/_matrix/client/v3/pushrules/global/postcontent/.io.element.msc4306.rule.subscribed_thread => 200 OK (182.735939ms)
      client.go:860: [CSAPI] PUT hs2/_matrix/client/v3/pushrules/global/postcontent/.io.element.msc4306.rule.subscribed_thread/enabled => 200 OK (9.276427ms)
      client.go:860: [CSAPI] GET hs2/_matrix/client/v3/pushrules/global/postcontent/.io.element.msc4306.rule.unsubscribed_thread => 200 OK (2.340842ms)
      client.go:860: [CSAPI] PUT hs2/_matrix/client/v3/pushrules/global/postcontent/.io.element.msc4306.rule.unsubscribed_thread/enabled => 200 OK (5.070549ms)
      client.go:860: [CSAPI] POST hs1/_matrix/client/v3/createRoom => 200 OK (289.701803ms)
      client.go:860: [CSAPI] POST hs2/_matrix/client/v3/join/!qFrSxZPtgSblQeZLrG:hs1 => 200 OK (523.969995ms)
      client.go:860: [CSAPI] PUT hs1/_matrix/client/v3/rooms/!qFrSxZPtgSblQeZLrG:hs1/send/m.room.message/1 => 200 OK (46.203508ms)
      thread_notifications_test.go:339: SendEventSynced waiting for event ID $UGkG73htT58nkjg7DMuxlOTbvWUd6JRAPYETSsQfqvI
      client.go:860: [CSAPI] GET hs1/_matrix/client/v3/sync => 200 OK (41.70729ms)
      client.go:860: [CSAPI] PUT hs1/_matrix/client/v3/rooms/!qFrSxZPtgSblQeZLrG:hs1/send/m.room.message/2 => 200 OK (28.757003ms)
      thread_notifications_test.go:346: SendEventSynced waiting for event ID $JDQ_oohdm0NDfd2Ea2xTuzAJDmV0GSfWMzTcAotEqKI
      client.go:860: [CSAPI] GET hs1/_matrix/client/v3/sync => 200 OK (13.279086ms)
      client.go:860: [CSAPI] POST hs1/_matrix/client/v3/rooms/!qFrSxZPtgSblQeZLrG:hs1/receipt/m.read/$JDQ_oohdm0NDfd2Ea2xTuzAJDmV0GSfWMzTcAotEqKI => 200 OK (14.356195ms)
      client.go:860: [CSAPI] POST hs1/_matrix/client/v3/rooms/!qFrSxZPtgSblQeZLrG:hs1/receipt/m.read/$JDQ_oohdm0NDfd2Ea2xTuzAJDmV0GSfWMzTcAotEqKI => 200 OK (6.825834ms)
      client.go:860: [CSAPI] GET hs1/_matrix/client/v3/sync => 200 OK (10.134173ms)
      client.go:860: [CSAPI] GET hs2/_matrix/client/v3/sync => 200 OK (28.158721ms)
      client.go:860: [CSAPI] GET hs2/_matrix/client/v3/sync => 200 OK (87.352601ms)
      client.go:860: [CSAPI] GET hs2/_matrix/client/v3/sync => 200 OK (541.749741ms)
      client.go:860: [CSAPI] GET hs2/_matrix/client/v3/sync => 200 OK (11.54514ms)
      client.go:860: [CSAPI] GET hs2/_matrix/client/v3/sync => 200 OK (1.005299683s)
      client.go:860: [CSAPI] GET hs2/_matrix/client/v3/sync => 200 OK (1.005586738s)
      client.go:860: [CSAPI] GET hs2/_matrix/client/v3/sync => 200 OK (1.005581281s)
      client.go:860: [CSAPI] GET hs2/_matrix/client/v3/sync => 200 OK (1.006382374s)
      client.go:860: [CSAPI] GET hs2/_matrix/client/v3/sync => 200 OK (1.006612323s)
      thread_notifications_test.go:370: @user-175:hs2 MustSyncUntil: timed out after 5.699962045s. Seen 9 /sync responses. Checkers:
          [t=28.3491ms] Response #1: SyncEphemeralHas(!qFrSxZPtgSblQeZLrG:hs1): Key rooms.join.!qFrSxZPtgSblQeZLrG:hs1.ephemeral.events does not exist
          [t=115.95164ms] Response #2: SyncEphemeralHas(!qFrSxZPtgSblQeZLrG:hs1): Key rooms.join.!qFrSxZPtgSblQeZLrG:hs1.ephemeral.events does not exist
          [t=658.056409ms] Response #3: SyncEphemeralHas(!qFrSxZPtgSblQeZLrG:hs1): check function did not pass while iterating over 1 elements: [{"type":"m.receipt","content":{"$JDQ_oohdm0NDfd2Ea2xTuzAJDmV0GSfWMzTcAotEqKI":{"m.read":{"@user-174:hs1":{"thread_id":"$UGkG73htT58nkjg7DMuxlOTbvWUd6JRAPYETSsQfqvI","ts":1783080803190}}}}}]
          [t=669.750815ms] Response #4: SyncEphemeralHas(!qFrSxZPtgSblQeZLrG:hs1): check function did not pass while iterating over 0 elements: []
          [t=1.675225765s] Response #5: SyncEphemeralHas(!qFrSxZPtgSblQeZLrG:hs1): Key rooms.join.!qFrSxZPtgSblQeZLrG:hs1.ephemeral.events does not exist
          [t=2.680951955s] Response #6: SyncEphemeralHas(!qFrSxZPtgSblQeZLrG:hs1): Key rooms.join.!qFrSxZPtgSblQeZLrG:hs1.ephemeral.events does not exist
          [t=3.686664064s] Response #7: SyncEphemeralHas(!qFrSxZPtgSblQeZLrG:hs1): Key rooms.join.!qFrSxZPtgSblQeZLrG:hs1.ephemeral.events does not exist
          [t=4.69319911s] Response #8: SyncEphemeralHas(!qFrSxZPtgSblQeZLrG:hs1): Key rooms.join.!qFrSxZPtgSblQeZLrG:hs1.ephemeral.events does not exist
          [t=5.69995822s] Response #9: SyncEphemeralHas(!qFrSxZPtgSblQeZLrG:hs1): Key rooms.join.!qFrSxZPtgSblQeZLrG:hs1.ephemeral.events does not exist, 
          
  2026/07/03 12:13:28 ============================================

Synapse Version

ab277b3

Database

Postgres

Workers

Multiple workers

Platform

Linux