Investigate duplicate events with default persistent subscription settings in Issue 1125 Test

[hayley-jean]

The test Issue_1125 fails when using the default settings when creating the persistent subscription.

When the settings are left as default, the persistent subscription in the test gets duplicate events at position 250. These events aren't retries, so it is possible that there are duplicate events being published as the subscription goes live.

To Reproduce
Steps to reproduce the behavior:

1. Remove the readBatchSize: 10, historyBufferSize: 20 parameters when creating the persistent subscription in the test.
2. Run the test on CI

Expected behavior
The test passes.

Actual behavior
The test consistently fails with 502 events received when it expected 500.

Additional context
This was discovered in PR #127