I use XMPlay's latest revision, and the SID 37.1 to play C64's .sid files, and for a few years, on three different systems (running Windows 8 and two Windows 10), I've experienced this oddity: when I want to convert the SIDs to digital, I set the output to a .wav file, and XMPlay does everything as it should, saving the music, proceeding from the SID's track #1 to the final track.
BUT: when the ready WAVs are opened, there is *always* a tiny "hole" in them, a very short gap of silence, in every track starting from #2. It is often found even in track #1. It always occurs at more or less 0.190 - 0.192 seconds of the .wav file.
I've no idea what the culprit may be.