Hola Javier,
I have added a JPG to FO with Lossy is enabled and Copy Metadata disabled. You've set the parameter --auto, so it would detect the best mode between CUDA, OpenCL and C-Opt. It looks like it chose OpenCL and the resulting file was empty and between 1 and 4 kB (from the original 400kB).
I tested the guetzi executable via CLI and got several dozen error line, all ending in CL_INVALID_KERNEL.
I imagine you could implement a way to detect whether the local machine supports CUDA, OpenCL or C-Opt, or you allow the user to set these parameters themselves. Either way, without a fail-safe way to identifiy the right mode (which guetzli apparently does not have), the default should probably be the original parameters (i.e. without --auto).
Just the make clear: in itself it is not an error of FileOptimizer itself.
FO version: 16.30.2781 (x64)
Plugin version: 2.1.5 CUDA