From Canon:
Notice Regarding the Phenomenon of Skipped Frames in Footage Recorded in Slow Motion on the EOS C300 Mark II Digital Cinema Camera
Thank you for using Canon products.
We have become aware that there may be cases of skipped frames in footage recorded in slow motion on the EOS C300 Mark II Digital Cinema Camera. Customer support for this phenomenon is described below.
We would like to offer our sincere apologies to users for the inconvenience caused by this phenomenon. Going forward, we will spare no effort in our quality management to make sure our customers can use our products with confidence.
Phenomenon
Except as provided below, footage recorded in slow motion in Slow & Fast Motion Recording Mode, in 4K and 2K/HD, and at all frame rates, may have skipped frames.
This phenomenon does not occur for slow motion recording at the following settings:
Affected Product
EOS C300 Mark II Digital Cinema Cameras with firmware version 1.0.0.1.00 are affected. The camera’s firmware version can be checked from [System Setup] on the menu.
Press the MENU button, then select [System Setup] --> [Firmware] --> [Camera].
Support
Canon has released new firmware that incorporates countermeasures for this phenomenon. Please download and install the firmware update.
Download Firmware Version 1.0.1.1.00 for the EOS C300 Mark II
B&H carries the Canon EOS C300 Mark II Cinema Camera.