Let's take the following campaign for example:
Overall, there are 400 leads in the campaign. Out of the 355 leads that have completed the sequence, only 49 messages were sent. This can happen because of any of the following reasons:
Leads didn't accept the connection request
The lead already replied
Similarly, only 294 follows were sent. Reason being:
Some are still in the queue
Certain profiles are locked, so LinkedIn rejects the follow request
Similarly for likes, certain profiles have no activity, so nothing can be liked.
We also stop the sequence when there is an ongoing conversation with a lead.
Lastly, out of the 400 leads, certain leads just failed to fetch. For reasons why, checkout this article.