Google Chrome version 61 introduced a bug where sticky elements would scroll away from you down the page. In Current RMS, this impacts:
The opportunity items list table heading
The opportunity detail view toolbar
This bug only affects high DPI screens, such as retina displays on Macs and some Windows 10 laptops like Surfaces.
Update Google Chrome to resolve
Google have released a fix for this bug that’s included in version 62 and above. Just update your version of Google Chrome by clicking the more icon (three dots), then choosing Help > About Google Chrome.
Google have a guide that runs through this in more detail, see: Update Google Chrome