I had a similar problem, I did report the text below but received no reply but I think it is related.:-
I found that in FST4W mode, if I select Tx Enable and Tx Next, although the PTT is activated, there are no transmit tones. If I select TUNE, all is well.
It seems I have to wait for the NEXT tx cycle before the tones come through. I reported this in -rc1.
Rig is Yaseu FT897D, Windows 7 home laptop. running wsjt-x v2.3.0-rc2. Cat control and audio via laptop mic and headphone sockets.
I actually connected a scope to the audio out from my laptop and observed no tx tones during ptt enabled and first transmission, my Tx was on but no output power (as in USB mode). When I got to the 2nd transmission (quite a lot later as I was trying FST4W 300 on 80m), tones were produced for the 300 seconds although I was unable to decode myself on a second receiver and 2nd laptop, At the end of transmission, ptt went off but there was a single tone still coming out of the audio socket, seen on the ‘scope. I had an evening of transmitting FST4W on 80m with no-one spotting me. A 2nd QRP Tx of mine running WSPR was heard all over Europe on the same evening.
hope this helps you diagnose the problem.
73 Ken G4apb