The Logo File needs to be stored in the same folder as the Planset / Drafting Template so that when you import the Planset Template the Logo gets found and it is copied into the Project Folder for the project.
If the Logo is somewhere else on your PC - it may show up in the Template when you created it because when you imported it to the Template the template stores the Path to the File (just like the project does), however when you import a Template into a project, that process is not looking at paths defined within the template and only looks for the associated files in the Folder where the Template was stored.
So move the logo file or a copy of it into the Drafting Templates Folder and then reopen your project and it should find it - for an existing project where you already imported the drafting template you may need to either
1) Delete the Drafting Template and reimport it or
2) Place a copy of your Logo File in the project Folder so t can be found with the existing drafting template
Alan