Canon r6 mark II card slot problem "Card cannot be accessed"

[Princejvstin]

I really can't figure this one out, so maybe someone has some ideas.

About a year and change ago, I  went from a Canon 5D Mark IV to a canon R6 mark II. Things went fine at first, but then I recently noticed I am having a bunch of SD card problems. I was getting the "card cannot be accessed" error

But its' frustratingly weird how the error happens:

It only happens in slot 1.

It only happens on cards larger than 64 GB. My 64 GB cards work just fine. I have a couple of different kinds of 128 GB cards in terms of manufacturers and they all act the same way. Any card larger than 64GB doesn't work in slot 1.

So if I take a 128 GB card and put it in slot 1, it gives me the error. I put that same card in slot 2, and it seems to work fine.

If I put one of my 64GB cards into slot 1 it seems to work fine.

I've tried formatting the cards, regular and low level format, to no avail. I've tried formatting the cards on a computer. No luck there.

And it is just slot 1. Slot 2, the 128GB cards work normal. Slot 1, "card cannot be accessed". But 64 GB cards work in slot 1, no issues. (and of course Slot 2, the 64GB cards work normal)

I even toggled the write protection switch on the cards back and forth. No dice.

It's as if my R6 Mark II can't "handle" a 128GB card in Slot 1. But Slot 1 can handle 64 GB cards. And the 128 GB card works in Slot 2.

I downloaded the latest firmware in hopes that would help. No dice.

Ideas?

[Princejvstin]

1. The cards work in Slot 2 but not Slot 1

2. I've restarted the camera dozens of times. 

3. I've tried formatting the 128GB cards multiple times
4. As I said in my post, 64 GB cards work fine in Slot 1. 128 GB cards do not. 
5. As I said in my post, I did that.  No change. 
6. I've tried this, with a rocket blower. Not sure why it would mean that "small cards will work" but larger ones won't in the same card. 
7. Again, if there was physical damage. why do the small cards work and the large cards don't? 
8. I have not yet contemplated this because I don't want to lose all of my custom settings. But this is a good idea. 

[Stephen]

We encourage you to acknowledge when you've used AI as your source of assistance, as it may not be completely accurate.

[Princejvstin]

Update: 

I bought a new 128 GB card. 

This card worked and works just fine in the slot, none of the card cannot be accessed errors. Took some photos with it (4th of July fireworks).  Yes, I also had a 64 GB card in slot 2 just in case this one was going to choke on me. 

So...is this a case of a whole set of cards that got semi corrupted? I...don't know.  I am going to keep watching and keeping watch on this new card to see if it "Corrupts" as well 

[shadowsports]

Greetings ,

I believe  I posted about something similar recently.  R62 and card requirements for recording high quality video. Recording media can be very important for reliability and performance.  

Although the R62 is backwards compatible with UHS-I, I would recommend UHS-II v60 and v90 cards.  It's more important for video , but this way you don't have to watch what you're putting into which slot. It might be wise to retire your aging stable of cards.  You can watch for sales at B&H, Adorama or your local Best Buy.  64 and 128 GB. UHS-II cards are more affordable than you might think.  Hopefully this will put an end to your strange card/slot behavior.