With the new Internal Comments feature, you can add comments on the Web App. However, those comments are not visible on the Contact Conversation detail within the Mobile App.

You can see the 'summary' of the comment when searching for the contact, but when you open the conversation there is a blank space. So, the mobile app is 'seeing' the comment, but not showing the comment to the user.

We have many sub-accounts that primarily use the mobile app, so such disparity in functionality between web/mobile causes friction.