Canon Rumors readers Darach G. (Darachphotography) has uncovered an issue with the Canon EOS 5D Mark IV that Canon themselves have confirmed. The firmware to fix the issue below should come within the next 4-8 weeks.
Darach G. explains the issue and how Canon handled it:
I was testing out the various remote control options for controlling video on my Canon 5d Mk iv. All works fine using the EOS utility V3 via WiFi or via USB and also using the Canon App on a samasung S7 phone. However, if you switch on the “High Frame Rate Movie” option and attempt any of the remote control options, the 5D Mk iv camera completely hangs. All functions including the on/off button become disabled and in one instance the camera actually “purple” screens. The only way to reset the camera is to take the battery and put it back in. Shooting high frame rate movie directly on the camera works fine, but remote control causes the problem. I upgraded the cameras firmware to 1.0.4 but the problem persisted.
I contacted Canon support in the UK and they immediately came back to me for some additional information. Within 24 hours of receiving the additional information, they were able to replicate the issue and escalated this the Canon Europe. I have since been informed via email that Canon Inc. are now looking into this and will attempt to correct the problem in a firmware update within the next 4-8 weeks.
Darach was extremely impressed with how quickly Canon acted on the issue, and has asked them name the firmware update after him. It's worth a shot.
Thanks Darach (Darachphotography)