I did online check-in about 8 days prior to our recent trip (arrived 10/4 at 10:30 am).
The system gave me the same messages as the OP. One of my choices the website offered for special requests was "full balcony". I selected that, then it said it could not process any requests at this time.
I then proceeded to the section where you enter the things you are celebrating on this trip, which appeared to go as it should.
When we arrived at the Beach Club, we were greeted outside by a CM who was expecting us. He walked us to the check-in desk, where he attempted to get the attention of the next available CMs, but they proceeded to help 2 other families who came in behind us. He apologized.
It took the CM who checked us in over 15 minutes to process things that should have already been ready for us. After that, she was handing us our celebration buttons, only to discover that my oldest daughters name was spelled wrong on hers.
Our room was not ready until 2:45 pm. It did have a full balcony, but I don't know if it was because of the request or just pure luck.
Long story short, online check-in that is designed to be grab and go took us over 30 minutes. Then we had to check our luggage with bell services, who wouldn't automatically deliver it to our room when it became available. We had to call for it from the room when we made our way back from Epcot.
