Shared reviews stopped working again recently. Many problems in many spaces. See these threads for details:

https://community.adobe.com/t5/acrobat-discussions/unable-to-post-comment-in-cloud-based-review/m-p/14101521#M430090:~:text=4-,Unable%20to%20post%20comment%20in%20cloud%2Dbased%20review,-Larry%20Kunz

https://community.adobe.com/t5/acrobat-discussions/unable-to-get-new-comments-on-shared-review-with-sharepoint-online/m-p/14099315/page/2#M429908:~:text=Unable%20to%20Get%20New%20Comments%20on%20Shared%20Review%20with%20SharePoint%20Online