EpocCam may no longer show up in Ecamm Live after updating to macOS 10.15 Catalina. This is because the latest version of EpocCam is required.
To fix this, download and run the EpocCam installer. This will update EpocCam to the latest version.
Once you've updated EpocCam, if EpocCam is in the Camera menu but not in the camera switcher, pick EpocCam in the Include in Switcher menu in the Camera menu at the top of the screen in Ecamm Live to re-add it to the switcher.