these gaps are nothing to be worries about. It is how Axon deals with the difference of insert-order (which defines the global sequence) and commit-order (which makes this sequences visible). Axon keeps track of these gaps to ensure that no events are ‘skipped’. When events are found, or the gaps are considered ‘expired’, Axon will remove them automatically.
This is most likely what you’re witnessing at shutdown. The processor stops, but events may still be inserted. That why the gaps seem to appear more at shutdown.
PS. Sorry for the late reply. It’s a travel intense time and most of the team are trying to get the 3.3 release out.