Firstly WOW! Just wow! What a fine piece of software! All the other forum producers must be quaking in their boots. From what I've seen so far, the software you've produced is just miles ahead of the competition.
However... We used the import function of xenForo to pull in the old vBulletin data. Everything went perfectly and no errors were displayed. The forums run perfectly, and all systems work. But there's a massive discrepancy between the number of members from the vBulletin set-up to the xenForo. Is there a known reason for this?