Based on my meager experience, and Experts suggest that "glitches" in the Dev Tools, when viewing the page on different from your resolution (320*568; 1920*1020, etc.) - a phenomenon quite frequent and common. You can spend the day searching - non-existent - errors in the markup and in css.
Question: please Tell me that You are using to see if adaptive layout?
To view (in native 1280*1024 resolution) as the page is displayed on the screen of 1920*1080 ?
If we talk about extensions (Resizer example), then in my opinion they don't properly display how the page will look like on the monitor with resolution 1920*1080, on your own monitor 1280*1024...?
And for Dev Tools to understand that at the present time this "glitch", not a bug in the code?