Faces created by Push/Pull are coplanar … always.
The root of the problem is subsequent modeling operations using techniques that invite and propagate errors.
See this copy of the file you shared:
FOR Q TO SU COMMUNITY_Modeling Issues.skp (1.5 MB)
• Persistent use of Inference Locking precludes off-axis modeling errors.
• Improper use of SketchUp’s Layer System is a sure path to modeling mayhem.
Unintentional alteration of raw geometry assigned to an invisible Layer can be one of the consequences.
In your example, the raw geometry of the wall is assigned to a Layer other than Default Layer0.