Canon EOS 5D MARK IV Instruction Manual page 561

The continuous shooting speed is slow.
The continuous shooting speed for high-speed continuous
shooting may decrease depending on the power source type,
battery level, temperature, flicker reduction, Dual Pixel RAW
shooting, Digital Lens Optimizer, shutter speed, aperture, subject
conditions, brightness, AF operation, lens, flash use, shooting
function settings, etc. For details, see pages 160-162.
The maximum burst during continuous shooting is lower.
If you shoot something that has fine detail such as a field of grass,
the file size will be larger, and the actual maximum burst may be
lower than the number listed on page 171.
If [Rec. separately] is set and different image-recording quality are
set for the CF card (Card1) and SD card (Card2), the maximum
burst for continuous shooting will decrease.
Under [z1: Lens aberration correction], if [Digital Lens
Optimizer] is set to [Enable], the maximum burst for continuous
shooting will greatly decrease.
If [z1: Dual Pixel RAW] is set to [Enable] and the image-
recording quality is 1, the maximum burst for continuous
shooting will decrease.
Even after I change the card, the maximum burst
displayed for continuous shooting does not change.
The maximum burst displayed in the viewfinder does not change
when you change the card, even if it is a high-speed card. The
maximum burst shown in the table on page 171 is based on
Canon's testing card. (The faster the card's writing speed, the
higher the actual maximum burst will be.) Therefore, the
maximum burst displayed in the viewfinder may differ from the
actual maximum burst.
Troubleshooting Guide
559