Why does HDMI out on my Canon 5D Mark III work with my TV but not my Lilliput monitor or BlackMagic Design Shuttle 2?
Some DSLRs output HDMI video that does not meet full HDMI specifications. It is not unusual to find combinations of source and destination gear that is incompatible.  The HDMI can be viewed on permissive screens (consumer TV receivers, etc.) but not on more professional gear that strictly adheres to the HDMI standard protocols.