“ General lock ups happen with Sandisk extreme pro 256 GB cards (two different cards, same type UHS1 V30 purchased at the same time from Amazon) and also the Kingston 128 GB UHS II v90 128 GB card. I've not had any lock ups or problems with the Kingston in my canon rebel SL2. “
I am going to point the finger of blame squarely on your memory cards.
First and foremost, I am going to assume that all your memory cards are full size and you are NOT using any micro-SD memory cards.
You should only use UHS-II cards with the R6 mark II. I do not recommend buying any camera accessories from Amazon, especially memory cards and batteries, due to the level of counterfeit products being sold as genuine.
Lastly, I will never again use Kingston memory devices. They are unreliable and prone to failure at any moment. I have had their memory stick thumb drives fail, as well as SD cards.
If you are in the US, then I recommend that you order SanDisk or Lexar memory cards from B&H.
12/05/2023: New firmware updates are available.
09/26/2023: New firmware updates are available.
08/18/2023: Canon EOS R5 C training series is released.
07/31/2023: New firmware updates are available.
05/18/2023: New firmware updates are available.
03/30/2023: New firmware updates are available.