Code object is not signed Subcomponent even though I have signed it (Developed via Unity)

I'm trying to upload a Mac application developed via Unity to the app store, but I get the following message:

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Unable to Sign - This package doesn't meet the current code signing requirements. For more information, see the Code Signing and Application Sandboxing Guide and Technical Note 2206.

Specifically, codesign generated the following error:

com.cyclopsgear.cyclopsdirector.pkg/Payload/XXXX.app/Contents/Plugins/libvlc.bundle: code object is not signed at all In subcomponent: com.cyclopsgear.cyclopsdirector.pkg/Payload/XXXX.app/Contents/Plugins/libvlc.bundle/Contents/MacOS/lib/libvlc.dylib

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Even though I have signed it (and its parent package) using codesign in terminal..

Here's what I have..

- The file the error is referring to is actualy the VLC media library (from UMP Asset).

- Here's the line I use to sign.

codesign -f --deep -s "3rd Party Mac Developer Application: XXXX" --entitlements "ENTITLEMENT PATH" "APP PATH"

- I signed every file that was received previously by mail, all problems with other files were removed except for the one mentioned above.

- Here's the line I used to build the package.

productbuild --component "APP PATH" /Application --sign "3rd Party Mac Developer Installer: XXXX" PACKAGE_PATH

- I use Application Loader 3.1

- Actually tried using 3.5 which came with XCode 8.3.2 but it kept saying that it's waiting for iOS app and the submitted is a Mac app, and with a little research found out that it was a known issue for this version so I switched to an older one.

- When I tried codesign -v it gave me the following message
Invalid Info.plist (plist or signature have been modified) In architecture: x86_64

What could be the problem?

Thank You,