IOMMU setting seems to be the root cause of Python-related multi-GPU training issues. By default, IOMMU is 'enabled', which causes multi-GPU training issue. DISABLING IOMMU resolves this issue.

Step 1 - Get to BIOS Settings

Step 2 - Navigate to Advanced → AMD CBS → NBIO Common Options

Step 3 - Set 'IOMMU' to disabled

Step 4 - Save Changes and Exit