It seems to be working perfectly fine for me.
I would try maybe checking permissions. If all is fine try clearing the cache on the browser and Tableau.
Clear cache on the browser
clearcache on Tableau Server
I think the issue has something to do with the settings in the internet options. As they have been set very strict, I need to know which rules must be enabled to allow adding comments.
I don't believe there are any "rules" to allow in regards to comments. Have you tried clearing the cache ?
If so, you could have your local IT try to open the developers console and see where it is blocking and see how to unlock.
You could also try to load it with another navigator ?
Another option is to get in touch with our support team that can go through the logs with you and troubleshoot, but they will most likely need you to have elevated rights.