@Ruediger_Brand There seems to be some connection to Cesium 3D-Tiles glb-files not visible in Unity - #5 by Marco13
When you have more specific information about the PLY data or the crash, then this might be investigated further. Cesium ion should be able to process Gaussian Splat PLY files. (There are some degrees of freedom for how PLY files are structured. In doubt, as a first analysis step, maybe you could post the header of these files here?)