This seems to be new, but while I can access the Forum's functionality on my Apple iPod Pro, I can't using my one-year old iPhone X. The X complains about 'flash-based commands', and won't allow me to respond to any messages! Also new behavior, on the iPad Pro, I'm only able to respond to a single message, after which the device freezes my ability to do anymore until I refresh the window.
I haven't updated either device lately, so I'm uncertain where this new behavior originated (it didn't exist a week ago!).