[Hummingbird] Can't run performance test -

Set Up:
- Site host is flywheel.
- Local environment: AppleOS 10.13.4 (17E202) and Chrome browser.
- This site uses the Avada theme (was cobbled together by my client).
- WPMU licensed and installed from WP Admin side rather than Hub (been having trouble accessing sites, updating
- I've removed as many plugins as I dared - no one knows what's really in use. There are still quite a few plugins to confuse things and cause compatibility issues.

Today's Issue:
I just activated the WPMU plugins: dashboard, hummingbird, smartcrawl. I want to run a performance test before I smush images and then after. The perf test runs but doesn't complete. Each time I get the following error message:

"The performance test didn't return any results. This probably means you're on a local website (which we can't scan) or something went wrong trying to access WPMU DEV. Try again and if this error continues to appear please open a ticket with our support heroes."

As I mentioned, I get a lot of these communication failures between WPMU and my WP sites. Is it my set up? Is it flywheel's security? Is it something else?

Please be my hero and help me get WPMU plugins working consistently.
Thanks in advance!