UserWarning: CUDA initialization: CUDA unknown error - this may be due to an incorrectly set up environment, e.g. changing env variable CUDA_VISIBLE_DEVICES after program start. Setting the available devices to be zero

ptrblck · August 14, 2021, 5:10am

This error is raised e.g. if your system cannot communicate with the GPU, which might be caused e.g. by a driver update without a restart or any other setup issue.
On my personal workstation I see this issue after waking the system from its “suspend” status, as this still does seem to cause such issues (after restarting it, it works again).