The issue was originally discovered while working on DBZ-2975: we've got some test suites reworked to test multiple databases being processed per task, and some of them started failing due to unexpected messages being produced:

1. SQLServerConnectorIT#testTableExcludeList
2. SQLServerConnectorIT#testBlacklistTable

We managed to reproduce the failures on the original codebase by adding extra assertions. Please see the reproduction details in https://github.com/debezium/debezium/pull/2280.

One of the newly added assertions in each test fails with the following error:

SqlServerConnectorIT.testBlacklistTable:961 expected:<1[0]> but was:<1[]>
SqlServerConnectorIT.testTableExcludeList:1005 expected:<1[0]> but was:<1[]>

The tests above should stream 5 rows of id's 10-14 but occasionally record with id 1 is seen twice: once in the snapshot record returned and again in the streaming records.

This issue is reproduced inconsistently likely to a race condition.