You may find in the core logs that the reason for the base images is because one, some, or all the protected volumes of an agent(s) is(are) in a dirty state. Creating the need to get a base image.
Follow these steps to confirm if the volume(s) of the protected machine getting base image backups is(are) in a dirty state and take corrective action:
Your backups should continue to be incrementals after check disk has repaired the issue on the affected volume(s).