Inconsistent Edge Length in Blender 2.9 Summary of Issue:
The Edge Lengths are inconsistently displayed on an obviously square object.
Issue Detail:
I'm still quite new to Blender.
Iam busy creating door frames using Cube, boolean difference, deleting the inner faces, capping the inner faces, and finally extruding the door frame out.
However, I've noticed some strange behavior. I'm sure this is by design, but it seems to have caused me problems now.
What I initially did was extrude, and type the measurement I wanted (0.004) for the door frame faces.
However, I realized that I actually needed to set it to 0.04 instead.
So instead of extruding again, I selected the faces and used the Move tool to specify my new measurement numerically (0.04) and hit enter.
It seems however that it appends the measurement using some unknown logic which doesn't make sense to me.
The side effect that I'm dealing with now in order to try regain consistency using &quot;Edge Lengths&quot; is that the edges of what is seemingly a square, is actually of different lengths.
I have no idea what is going on, however I can only find help on this for Blender 2.8, and apparently the entire application UI changed within a single minor version number.
Please may somebody help me out here.
This is what I'm talking about:
I can't be sure this is your issue, but overlay 'Edge Lengths' are displayed in Object space: that is, before any Object-level transform the object is carrying.
This plane has been scaled by 2 in Edit mode, doubling its vertex X-locations in Object space. The rectangle has then been scaled by 0.5 in X, in Object mode, restoring it to a square in World Space, but only by virtue of the transform the object is carrying.

If you CtrlA 'Apply' the scale-transform of the object, that will reset the object's X-scale to 1, and bake the object's scale into the Object-space locations of its vertices.
(The shipped add-on MeasureIt displays dimensions in World space.)