The current "'dcraw.exe' v9-27" used by SNS-HDR does not support the 5D-Mk4... ...a dcraw update from DCoffin is needed and is not yet available.
Current supported camera list may be found towards the bottom of the web page here:
http://www.cybercom.net/~dcoffin/dcraw/Suggest using an alternate raw converter [Canon's DPP with its available specific camera/lens aberration corrections] and importing the resulting 16-bit tiffs into SNS-HDR.
...den...