AutoCAD has the ability to set the visibility status on individual objects to True or False. When you save the DWG and then open it in TBC, TBC honors that setting and does not display the objects. We don’t see this data setting that often but it does happen.
So if you cannot see the objects you cannot select them manually (unless you use a global selection like CTRL A (All) which picks everything (visible objects on visible layers as well as objects that have the visibility flag true or False that are on a visible layer)
Use “Ctrl-A” to select all the data (including the lines “invisible”) and then hold the ctrl key down while you do a window select of all the data. The control key will toggle the select state so you end up with just the lines not visible. You can then use the properties of the hidden selected objects to change the visible state to “true”.
Now you can see them and do what you need to do with them.