As of the 7th of January, we have released Axon Framework 4.5.7.
This release contains a single fix.
Namely, pull request #2067.
This pull request solves a bug that had the PooledStreamingEventProcessor not handle new events resulting from an EventMultiUpcaster.
The kudos for spotting the bug go to Magnus Heino, which started a discussion on our forum after he noticed the issue.