Why is my artifact count smaller after I upgraded my Artifactory to 3.x?

The difference in the number of artifacts you see right after the import to 3.2 is due to the fact that Artifactory exports do not include the cached items generated by virtual repositories (such as pom files). This explains why the artifact count in the new 3.2 instance might be lower than in the original 2.6.6 instance.

So this situation is normal and no data should have been lost during your upgrade; however, if you want to be certain of this, you can check the logs for any errors/warnings during the import. Another way to verify that nothing was lost in transfer is to run the File List REST query on a repository in both instances and compare the results.