Do you get any error (other than what you included earlier)?
Try setting it to Notes rather than blob first and see if that works (this will tell you if it is something specifically with the setup for blob storage or not).
Make sure you have cleared the Portal Cache after making these types of updates to the Entity Form etc.
Double check the users entity permissions has them for (Notes/Annotations and the entity that will be the regarding object and that Append/Append To are set on)