Subassembly Can Not be Placed on "Left" Side of New Assembly using Existing C3D Drawing - Civil 3D 2020

[jamesloy22]

I am using C3D 2020 in an existing file that I have been working on for months, it has multiple assemblies and multiple corridors. I want to create a brand new assembly that has subassemblies on both the left and right side of the assembly. For some reason when I have the "LEFT" side active in the properties window (before I place the subassembly on the assembly), it can not add the subassembly to the assembly (the length is not zero, it is not on an frozen or turned off layer). If I change the side to "RIGHT" on the properties, it has no issues adding the subassembly. This is the same issue for multiple subassemblies that utilize the "SIDE" property, like linkwidthandslope, LanesuperAOR, BasicLane, etc. 

I started a new drawing using the same template file to test and it does not have this issue. It is a file issue not a program issue, but I have attached my specific product version info for reference. 

I can not share the file to demonstrate the issue. I tried purge and audit but it didn't make a difference. Has anyone else had this issue or know of a solution? 

[MSchille-1994]

Can you copy a Left Side Sub-Assembly from a different Assembly to the Assembly you want it in?

[jamesloy22]

No I can not copy or move an another left side subassembly into my new assembly (using the ribbon buttons). I can add another LEFT side subassembly to an existing assembly I have IF that assembly already had a subassembly on the left side prior (I originally made the assemblies months ago and didn't have this issue back then). If i try to do a simple copy / paste of an older assembly (with subassemblies) it crashes my Civil 3D. 

[Udo_Huebner]

As we can see in your picture, you have not yet installed any of the available C3D 2020 and AutoCAD updates. In fact, they are not available in your account since May, since 2020 is no longer under subscription. Does this problem also exist with updated C3D 2020 versions (or newer versions)?
If you think it's a file problem, how about pasting the entire drawing into a new blank template file?
If you have a subscription, you can upload the drawing to the Autodesk Support team for investigation. They will keep your files confidential.

[jroot]

Can you build the right side and then Mirror it to the left?