If style lock is off, it uses the symbology of the dialog box settings to display. If it is on, it uses the styles saved in the drainage database. These can be reviewed in the review edit drainage structures - I do not recall which tab.
If these are not assigned properly, you will get strange results. Look at the settings as you walk up and down the structures. You will probably find that those that display have something defined different from those that do not.
I have been working at modifying a client structure definition file to include some generic existing structures with dashed line symbologies and also assigning symbologies for proposed. It has been a while. Here are some lines pasted from it:
;(dia) x Thickness - in x in)
; Center Feature Style Inside Feature Style Outside Feature Style
RCP, Class IV, B
12.00 x 2.0000 PipeProp_12" DR_pipeProp_Walls DR_pipeProp_Walls
15.00 x 2.2500 PipeProp_15" DR_pipeProp_Walls DR_pipeProp_Walls
EX. RCP
12.00 x 2.0000 PINVA TO_Ex-SD-Pipe-Wall None
15.00 x 2.2500 PINVB TO_Ex-SD-Pipe-Wall None
18.00 x 2.5000 PINVC TO_Ex-SD-Pipe-Wall None
21.00 x 2.7500 PINVD TO_Ex-SD-Pipe-Wall None
Circular ; (manholes)
Standard
; Max pipe size Diam x Thickness Point Feature Style Inside Feature Style Outside Feature Style
; (in) (ft x in)
;-----------------------------------------------------------------------------------------------------------------------------------------------
24.00 4.00 x 5.0000 DR_structProp_Walls DR_structProp_Walls None
36.00 5.00 x 6.0000 DR_structProp_Walls DR_structProp_Walls None
48.00 6.00 x 7.0000 DR_structProp_Walls DR_structProp_Walls None
Existing ; (manholes)
; Max pipe size Diam x Thickness Point Feature Style Inside Feature Style Outside Feature Style
; (in) (ft x in)
;-------------------------------------------------------------------------------------------------------------------------------------------------
33.00 3.75 x 8.0 TO_Ex-DrStruct-Wall TO_Ex-DrStruct-Wall TO_Ex-DrStruct-Wall
EX. MH
; Max pipe size Diam x Thickness Point Feature Style Inside Feature Style Outside Feature Style
; (in) (ft x in)
;------------------------------------------------------------------------------------------------------------------------------------------------
39.00 4.00 x 8.0 TO_Ex-DrStruct-Wall TO_Ex-DrStruct-Wall None
Some of these draw simple lines. These can draw pipe or structure edges in plan, profile or section. Some draw wide lines using a custom line style - these are for pipes and culverts in plan view only..
Style None is set to display nothing in plan, profile or section. This keeps a stray default from displaying anything. It actually uses the symbology of Default, but since the surface settings are all off, it works to draw nothing.
These are Styles that must point to named symbologies. In the dialog boxes, I am not sure if they call them styles or symbologies - they are feature styles however.
The structure definition file I started with did not have all of these columns. Once you assign some styles, the columns change. But then you can bulk edit them in an editor, if you are careful. I generally assigned styles to one of each structure and then, in the editor, I copied and pasted that symbology to the others.