There can be many reasons why app is showing error message in comments. Some of the main reasons are:
Admin has deactivated comment for that card: Sometimes it may happens that the administrator of your organisation/channel has inactivated comment function in a card at the same time you are looking at the comment. To fix this issue, simply refresh the app in news feed or re-start the app after completely removing the app from the phone background.
No Internet connection: User can only comment or read past comments with proper internet connection due to security reasons. Please make sure that your device is well connected to the internet
Syncing issue between the app and tchop database: Sometimes, there is some delay on syncing of app and tchop backend. Please restart the app and the issue at hand should be fixed.
If the problem still exists and you think there is some other issue, please write to us at email@example.com and we will take care of it