App Migration is not triggered (onStartAppMigration method is not invoked)

[Neelakanta Reddy M]

When we are testing our app migration since yesterday we are not able to get events from CloudMigrationListener. Observed some exceptions in atlassian-jira.log.

com.atlassian.jira.migration.httpclient.exceptions.UnexpectedStatusCodeException: Received an unexpected status code; expected [200], but received 504:
at com.atlassian.jira.migration.httpclient.exceptions.ExceptionsKt.unexpectedStatusCode(Exceptions.kt:7)
at com.atlassian.jira.migration.httpclient.AbstractPluginHttpClient.checkExpectedResponseCode(AbstractPluginHttpClient.kt:134)
at com.atlassian.jira.migration.httpclient.AbstractPluginHttpClient.execute(AbstractPluginHttpClient.kt:63)
at com.atlassian.jira.migration.httpclient.AbstractPluginHttpClient.execute(AbstractPluginHttpClient.kt:51)
at com.atlassian.jira.migration.amsclient.DefaultAppMigrationServiceClient.registerTransfer(DefaultAppMigrationServiceClient.kt:89)
at com.atlassian.migration.app.AbstractCloudMigrationRegistrar.lambda$startMigration$4(AbstractCloudMigrationRegistrar.java:96)

Please let us know if anyone knows the solution