several issues after 4.9.2 update

After my site auto updated to 4.9.2, my site started having issues. Page loading is extremely slow. Anything I add to my quick CSS will not take effect, my advanced styling will not make changes, my header settings all changed in mobile view. My font colors changed to default. My menu title font became smaller (tried to make them large again using quick CSS and advanced styling, but nothing happens).
I’m not sure why this happened. All plugins are updated, my theme is updated. What else could be causing this? Do I need to talk to my theme developer? Even though it happened right after the WordPress update? Thank you!

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