Canon have released firmware v22.214.171.124.00 for the C100 Mk II that “Fixes the phenomenon in which the aperture adjustment may not operate as expected when using the control dial on the grip unit when certain EF lenses are attached. This occurs with EOS C100 Mark II cameras running Firmware Version 126.96.36.199.00.”
Sounds like an issue worth avoiding…
The advisory notice on Canon’s site says that the fix is only for cameras running firmware versions between 188.8.131.52.00 and 184.108.40.206.00 – if you’re already on v220.127.116.11.00 you don’t need to apply this update.
For a full list of the lenses affected and the download link, head over to the Canon product advisory page.