The topic was expected to discuss during this past week’s city council.

このトピックは、この1週間の市議会で議論される予定でした。
The topic was expected to discuss during this past week’s city council.

答え
discussをbe discussedにする

The topic was expected to be discussed during this past week’s city council.

discussに目的語ないのはおかしいし、意味的にもトピックが議論するというのもおかしい。