I have a suggestion for this common problem, where Hummingbird enables Gzip compression, but then fails to detect it as correctly enabled.
I've used these three websites to check and confirm that Gzip compression in fact is enabled, and Hummingbird isn't detecting and reporting this correctly:
I have a suggestion. Wouldn't it be better and more robust for WPMUDEV to set up their own hosted Gzip checking service and send the request to that URL to test a site? Then receive back the enabled/disabled response from the site? This would surely be much more effective that trying to test this inside the plugin from the same site where this doesn't seem to be consistent at all.
I'm not suggesting a public service like the ones listed above. But a simple service for Hummingbird to interrogate.