This is a normal behavior of IMSVA when any of the below conditions are encountered.

Scenario 1:
If one sender sends to email to recipients with multiple domains, the mail will be split and it will be delivered based on the policy of IMSVA.

Scenario 2:
For example, if one email is sent to 2 users, the first one is user1@test.com, and the other is user2@test.com .
If IMSVA has a policy that only applies to user1@test.com, and the action is to modify the email. Then the message is split.

And in the message tracing, there are 3 records:
1. Message is split (you can ignore this record)
2. user1@test.com is delivered or quarantined...
3. user2@test.com is delivered or quarantined...