Load time sluggish due to custom code

When working on my site pages in Squarespace, I am suddenly having to wait a minute or more for any selected page to populate so that I can work with it. What I see in the bottom of my screen is that Squarespace is "waiting for trackcmp.net"

And once I finish and click Save Changes, it again is taking more than a minute for the page to resolve. Everything just goes blank. On my live website, everything is fine.  In a chat with Squarespace I was told:

"After looking at your site in the editor I see what you mean. I've viewed both with and with the code disabled, and it seems the issue is your code. When viewing the site with the code enabled, it is taking a long time to load, however with the code disabled it loads right away."

Can anyone help me find the problem?

What custom code do you have on the website?