Sometimes, most times, when Im leaving feedback via my phone, it does the exact same thing. I get home and leave feedback via my Laptop, no problem.
I dunno why it works, it just does. So I dont fight it. I just post feedback from my Laptop most times, because it lets me. Not saying occasionally I cant get away with it on my cellphone, but most times "No Joy".
Scott/Frontline, An "Unapologetic Habitual Feedback Leaver".