Internet speed

For a few days now, the internet connection has been slow.

Did a speed test today, within a minute apart, first with Xfinity, then Google Fiber, and finally with At&T.

We have a basic 500 Mbps plan, and Xfinity says the connection is "getting 119% of your plan speed."

But, the other two speed tests say otherwise.

Google test says download speed is 221.3 Mbps.  AT&T reports 254Mbps.  In other words, we are operating at 50% of our plan speed.

What's going on?

Why is our connection slow, and why is Xfinity's test result far different from the other two?

I have screenshots if anyone is interested.

Thanks