In addition to the SBSRender command you thoughtfully included, I would like the following information:
What environment are you using to check the exported images: importing them back into Designer, loading them into a specific image viewer, some other environment?
Open the Edit menu and select the Preferences option. In the Preferences window, select the Projects section. In the Project files list, select the last item listed, then select the General tab and scroll that section to find the Image format settings. Select the EXR tab and let me know if the Use Float setting is checked
Please share the Substance 3D file (SBS) and bitmap resources involved in reproducing the issue on your system