All Frames use classes for the vast majority of styling. If you notice that styling is applied to the ID of a frame, take a moment to analyze the styling.
If the Frame is a unique Block-level Frame being used as the child of another Block-level Frame, we most certainly used ID styling to adjust the frame for this unique use case while protecting other instances of the Frame from receiving the same adjustment.
If the Frame is not a unique Block-level Frame being used as the child of another Block-level Frame, it’s quite possible that a mistake was made when creating or editing the Frame. If you think the ID styling is a bug, please report it in the support community so we can fix it.