When exchanging InstantLinks, the number of automatic exchanges plus the number of invitations sent is sometimes fewer than the number of sites I selected. Why?

Sometimes LinkMachine cannot reach a site that you select to contact for an InstantLink exchange. This can be because the site has recently uninstalled LinkMachine or has not upgraded their LinkMachine account to Premium and their free trial has run out. It can also be because the site is temporarily inaccessible, or (rarely) because of connection problems with your own web server that prevent it from reliably accessing external sites.