I have had some issues with volume also with BitPerfect. Recently I realized that the slider bar on iTunes was at half volume and it may have been from using the keyboard volume (up/down) while using Google for video while listening to music via BitPerfect. With BitPerfect we want the dedicated output (USB, etc) to be at max, but the computer speaker volume at a lower level. If playing with those volumes doesn’t help, I suggest contacting BitPerfect directly.
With respect to pauses between tracks, I occasionally have the issue with specific “live music” tracks yet most are gapless. Don’t know why but I let it slide as I hope to get a new server soon and leave iTunes and BitPerfect behind forever… I used BitPerfect for a few years, then Roon for a couple, then realized that Roon did not sound as good so I did not renew it. I have another glitch with BitPerfect (track often will not play on first try) and have always found it’s not a perfect app, but have put up with some issues because it sounds vastly better on my system than iTunes.