Do you have any audio with that garbled picture?
All systems use RGB Scart into the OCCS and all others are working fine.
Then the problem is (most likely) related to the SNES itself… since the HDMI connection seems to be fine and an analog RGB connection can’t produce such kind of picture distortion. I would rule out wrong OSSC settings too… except your TV has such crazy reactions for feeding it with “strange” resolutions (did it happen with every scaling option: 2x-5x?).
If possible you should check the picture with an analog TV to find out, if your SNES already outputs this garbled mess. And do some tests with different game cartridges (since the cartridge could be broken… or the the cartridge slot could be dirty). Even if your SNES is the culprit, different games can give a hint on what’s broken because of the hardware functions they use:
http://projectvb.com/nss/logs.htm