I've been shooting with confidence with these cards on my GH4 (64 GB Class 10, SDXC I, U3, R95, W60MBPS) over the last year.

I remember one time about half a year ago that I couldn't record because I got the 'this card is too slow' message. But after shutting the GH4 off and on it worked and I never had this message again.

Now I've got this message twice in the last week. Can a card degrade in a year? Or should I use different cards altogether. I don't mind paying more as long as I don't see that dreaded message again!

Or is this just a risk you take with this prosumer camera, regardless of cards used?

Which cards have worked flawless for you for an entire year?

Yes, a card can degrade. I have had decent experiences with SanDisk Extreme 64GB 60MB/s cards running 24MBs on my GH3/GH2 and 35MBs (XDCam). Assuming that you have been using the GH4 at 4K you could be pushing the cards. Generally 32GB cards are considered more stabile than 64GB cards although that should change in time when 128GB cards become more common.

Try SDFormatter. Do a full format on the card & see if that fixes your issue. In time, if you only delete clips, & or do a quick format, the card can bog down.
Hope this helps,
Bryce

Thanks, guys. Yes, I was recording 4K, that's all I shoot except for the occasional slomo... I'll try SD formatter- makes sense that it bogs down. The same way you need to do a fresh reinstall of the OS on your PC after five years... (has anyone ever... ;-)

I'm using the same cards too and yes, absolutely do a low level format at least every 6 moths (depending on usage) You will also find the capacity drops a bit over time and SD formatter fixes all that!!!

I even give my 16GB transcends a run thru SD Formatter twice a year !!!

Unfortunately, a day after the deep format I still got the error message again... Guess that's going to be my 'vacation card'...