nadegea Hi
Had posted the solution after replicating the same on local install. Ref: Screenshot where the "read more" tab renders fine after adding the specific php code in template override file
I can see the code being added fine in respective attached file however, merely impossible to review, check and diagnose without having closer look by way of live site url.
You may also check if file permissions are set right for respective file/folder to be either chmod 777 or 755