I think they added a scrollable button area to the dialer. Try dragging the buttons upward to see if the record call button appears.
RTT is for "Real Time Text", which from what I can tell, is basically a hybrid form of communication that carries text messages over an open "phone call" for disabled people. Its distinguished from regular text messages in that it can work through a business call center and route the messages to whoever the phone call is routed to. The RTT button will only show if both ends of the call support it, which is why it appears intermittently.