WP Hummingbird

The Hummingbird plugin was active from about 3 weeks ago and then we were making some custom work and noticed that the edits not appears due to the plugin so we deactivated it

Yesterday suddenly the site become very very slow (almost unreachable) and if the loading finish it opens with different font, so we tried to activate the plugin again

After activating it, the site speed become good and the font also become good, but the plugin change the background of the header to black while it is white the theme options, i tested to change it (by force) in the inspector and it could be done but when applying the changes to the CSS files it still appears black

When we deactivate the plugin and while the page loading, in the bottom of the browser showing "Waiting For http://www.fontstatic.com..." and last long time till the page open http://prntscr.com/brwc5r

image of how it looks in our side when we deactivate the plugin http://prntscr.com/brwafw
Can you please advice, looking forward for your reply