From Mike Evans on the Vatsim development discord:
So it looks like swift is transmitting on 131.570 instead of 131.575
and the controller isn't able to receive text comms from that pilot..
the pilot is tuned to 131.575 in their plane
and can receive text messages from the controller, but when they go to reply, the controller doesn't see the response.
And from Collin Koldoff:
More recently facilities have been shifting away from dropping the 5, most facilities that do tx/rx on both frequencies per their SOP
From Mike Evans on the Vatsim development discord:
And from Collin Koldoff: