I use a Logitech Brio 4k Streaming Editon for Xsplit. The image captured by the webcam sometimes flickered a lot when using XSplit VCam. After much research, it turned out that it is due to the data transfer between the webcam and the PC. The cable supplied by Logitech has too high a resistance and this results in sometimes strong flickering of the image recording.
Solution: I bought a 10 GBit USB 3.1 (gen2) - USB-C cable and replaced it. Since the change, XSplit works perfectly.