A few Ecamm Live users using an Elgato Facecam have reported problems with image quality or frame rate when using this camera with Ecamm Live. Changing the USB Transfer Mode setting in Elgato's companion application, Camera Hub, has solved the problem for those affected.
The default setting according to Elgato's support site is 'Automatic'. If you experience image quality issues with this camera, try choosing the specific setting recommended by Elgato Support for your Mac platform:
M1/M2 Mac - 'Isochronous'
Intel Mac - 'Bulk'
For more information, please see this article from Elgato's support site.