Very long "Time to first byte" times for sites with Domain Mapping.

Hello,

I'm having an issue where many of my domain mapped sites on my multi-site installation take 10x (1sec/kb vs 0.1sec/kb for other sites not domain mapped) longer to load. Running it through some load speed testers it looks like it initially takes 20 or more seconds for "time to first byte" then once started loads as fast as you'd expect.

I've tried network disabling the domain mapping plugin to test if it is the cause, however even disabled I am able to browse to my sites by their mapped name which makes very little sense to me.

One of these sites is maax-collection-hot-tubs.com (maaxspas.biz/maax-collection/).

Is this something you've seen before? Anything you can do to help me pin this issue down?

Let me know if there is any other information I need to provide to assist with troubleshooting this.

Thank you.