Thank you for your response.
In the case, if the issue applies to other solutions and since the templates are present in the folder, the reason could be that the IDE cannot read these templates properly.
I kindly ask you to replace the existing templates in the 'Apex Code' folder with the attached ones. Please follow the next steps for this:
1. please download the attached archive and unzip it;
2. close the IDE;
3. open the 'C:\Program Files (x86)\The Welkin Suite\The Welkin Suite\ItemTemplates\SalesforceProject\Apex Code' folder;
4. replace existing files with the files from the archive.
After this, please launch the IDE and check if the issue would be reproduced
Also, can you please tell me if templates from other folders (like Lightning Bundle, or Visualforce) are available for you in the 'Add New Item' wizard in the IDE?
Looking forward to your response.