Try A0-5
I don't think it's that we want to inhibit the APRS transmit, it's that we don't want the incoming audio on the band to be muted right? When my radio Xmits an APRS beacon, it interrupts the incoming signal from a QSO in progress on the other side of the radio like you say above. It's pretty brief, but I wonder if changing A0-5 to something OTHER THAN TX MUTE or TRX MUTE would solve this?
I would paste a few words from the manual in here but of course Yaesu locked the PDF so you can't cut and paste from it which is a PITA.
Anyway, I will try this, but I suspect that's what is going on. See page #32 top of the U.S. FTM-350 Op manual. I think the function is similar to what I had on 2 Kenwood mobiles....if you are talking on 440 on the right band and a signal is received on the left band say on 2M, then in order to prevent you re-transmitting that 2M audio into your QSO on the 440 side [l;et's just call it that for now] the TX (or TXR) Mute stops the audio output where you are receiving. This is usually good, because you're generally RX-ing and TX-ing on the same side, and the 'other' side of the radio is just RX. Not so with APRS, it's Xmitting right? And we've told the radio "If I am Xmitting and there's audio on the 'other side' then mute that side." ...The fact that it's the RX audio from net control in your in progress QSO is not known by the radio...I suspect it's just doing what we told it. I'm going to switch to A0-5 = OFF and see if this becomes a non-issue.