Source: 44.1 kHz
OS Mixer: 48 kHz or higher (typically)
No sample rate conversion to the OS Mixer frequency configured in Roon?
Does configuring a matching sample rate conversion in Roon or changing the OS Mixer frequency in Windows to match the source resolve your problem?
Since you are using a Windows PC, I would verify that both Roon.exe and RAATServer.exe have been added as exceptions to your Windows firewall.
You can use these instructions to add the exceptions and the executables themselves would be located in your Database Location/Application folder path.
I would also add these exceptions to any Antivirus or other Firewall blocking applications you may have and ensure that you connected to your network via a Private network, not a Public one, see this guide for more information.
What DAC do you have connected to the non-working PC, is it this one?
Sometime bluetooth headsets are picky about what type of channels they accept, I have seen some headsets only take 5.1 or 7.1 channel content, so you would need to configure this in Device Setup.
I would also try to enable DSP upsampling to see if other sample rates work, you can specify Max PCM rate or custom re-sampling in the DSP menu: