Regarding HQ Player: you are not in trial mode, I assume? During trial HQ Player will only work for 30 minutes, after which you’ll have to restart you SonicTransporter.
Also, I assume you use HQ Player to upsample. Have you checked your system status, to see if your SonicTransporter can actually deal with your settings?
To confirm, does the stoppage typically occur when you bring your iPad awake from being idle?
Let’s refresh your RAATServer database and see if your issue persists.
You can generate a new RAATServer instance on your device by following these instructions, but please be aware that this will reset your Roon Settings → Audio Tab to factory settings and I would advise making a backup of any custom DSP settings you have: