Sometimes when I use WSJT-X even on RX the signals on the waterfall appear smeared and I get no decodes. I have selected the default audio device. Most times this is fine and I see many decodes. When I select USB Codec all is fine. The photo shows the effect.
I use a SignaLink USB interface with the FT817ND as I have done for many years. I am using the latest fully released version on FT8. I was not aware of issues with earlier versions.