domain mapping not working correctly

I have three domain names that are not mapping correctly to three different subsites in my multisite environment.

Sometimes they direct properly, some times they do not. They have a better likelihood of directing properly when I enter http:// in the browser, but that doesn't always work (and I've cross checked this on three different browsers). Two of them are being redirected to mainsitename.com/client_center/ which is a whmcs page. That page is assigned within wordpress as the default homepage of the multisite environment. They should be going to subsite1.com and subsite2.com respectively. The third domain name is being redirected to mainsitename.com/subsite3 instead of subsite3.com

I've verified that the A records are configured correctly.
And I have tried all three options available within the domain mapping plugin (e.g. "disabled and entered domain name should be used", "directed to mapped (primary) domain", and "directed to original domain") with no notable difference in the outcome.

Any ideas?