I am afraid that it is hard to determine the exact cause of the problem without examine the problematic configuration on our side. Can you, please, follow the steps from this blog post and send us a runnable sample reproducing the case, so we can continue the case investigation on our side?
Meanwhile, I would advise that you review the ThemeBuilder's documentation and make sure that you have followed all instructions listed in it:
Looking forward to your reply,
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and share your thoughts.