One of the many possible explanations for this behaviour is that the report might be critical of the clerk and somebody might be shielding him/her from the criticism. It's very unlikely that an IA would charge the council for sending an email, for two reasons. Firstly, they would want their report to be available to all. Secondly, if they add further charges, they run the risk of being replaced by another IA.
The role of the IA is not just to work for the council for a day or two after the end of the financial year. They are appointed to serve for the whole year and can be involved whenever required to support the work of the council.
This is a council that appears to have lost its way, but this may not be a grand conspiracy. My starting point is always to point out procedural errors in the hope that they may be rectified.