Cloudflare proxy causes increased Time to Interactive (TTI) & Total Blocking Time (TBT)

[t.s]

I have two versions of my site up on the same server, one on a staging subdomain that is not proxied or cached by Cloudflare and the other on the main domain, that is proxied and cached by Cloudflare. I am seeing a consistent increase in Time to Interactive (TTI) and thus Total Blocking Time (TBT) on the main site proxied and cached by Cloudflare. I am seeing on average around a 15% increase in TTI.

I am seeing this from Google Page Speed Insights, WebPageTest, and PageSpeed Compare.

Here is a link to the Cloudflare proxied/cached main domain WebPageTest

Here is a link to the unproxied/uncached staging domain WebPageTest:

As you can see there’s a 119% increase in TBT but all over stats are favorable.

I have Cloudflare’s RocketLoader turned off, as it was hindering performance.

What is causing this? How can it be fixed?

[t.s]

The answer was that I had “Bot Fight Mode” and “Email Address Obfuscation” enabled, which were both causing massively high TBT times. I still have a slightly higher TTI but I can live with that.