I formatted the ss card on my PC with exFAT but the camera wouldn't recognize it and I formatted it on the osmo action 3.  When it was done successfully formatting it then also said failed after confirming the successful format.  But the SD card still worked anyways inside the camera.  I took the SD card out of the camera and put it in my PC and it said the SD card would need to be formatted (I do this with numerous other cameras and SD cards, so it isn't a PC issue).  I then put it back in the camera and hooked up the camera directly to the PC and could transfer files over no problem.
Does the format for the SD card just not work with windows?  What format does the camera use?
Thanks.

Once you get all your files off and safely backed up, I would recommend you format the card in the camera again and see if you get the "failed" warning again.  If not, just take a quick test video and see if it will read in the computer.  My guess is that something was partially corrupted and it's affecting the computer's ability to properly read the card.  Just a thought.  But I'd try formatting again or even try another card.  I've gotten bad cards, even name brand ones.  Some of them work, but cause odd issues.  I had I had a brand new micro SDXC card which seemed to work fine, but it had a defect that made the battery life of the device it was in dramatically lower.  I'm talking minutes instead of hours of battery life.

I'm not saying it's the card, just that I'd try a few things to see if you can confirm the source of the issue.

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Hi there. Thank you for reaching out and we're sorry for the trouble that this has caused. Can you please confirm what specific SD card are you using? In addition, could you please try to use a different SD card for us to further isolte the issue? Please keep us posted. Thank you.