I am experiencing a similar issue to the one described in this forum post: Audio2Face headless background play issue - Digital Humans / Audio2Face - NVIDIA Developer Forums.
When I run Audio2Face (A2F) in headless mode on a Linux Server via the .bat script, I occasionally encounter robotic sound issues. These distortions sometimes occur at the start when the streaming player begins, or during playback of longer audio files. However, this issue only affects the client side (Unreal), running on a different device. When I listen directly to the audio output from the Linux server, it plays perfectly without any problems.
Both the server and client devices are using the same sample rate.
Interestingly, this issue does not occur when the Audio2Face application is running in normal mode (with UI), where the audio streams to the client correctly without those robotic sound issues. It only arises when running in headless mode.
In contrast to the issue described in issue 288783, where both applications (Unreal Engine and Audio2Face) were running on the same device and potentially interacting with each other, my setup is different. In my case, the Audio2Face application is running on a separate server entirely, with no other applications (such as Unreal Engine) running alongside it. This isolation should, in theory, prevent any interference between applications.