I had the same issue after updating to the latest firmware on 2 HD2's, I had a lockup on one camera straight after the update scrolling the menu. Then both cameras locked up when I was recording some video, I did a 3d quick video test with no issues but when I tried both cameras on their own they both froze during recording.
I thought it was firmware related but maybe SD card corruption. For this to happen to 2 separate cameras with different SD cards I thought it was quite odd so I tried reformatting them properly to see if that would fix this issue.
I did a full PC format of my SD cards and since I have had no issues completing about 10 full battery cycles with video recording and no issues since. Make sure your set the same parameters as in this pic below and do a full format rather then quick.
I don't know if this corruption occurred while doing the firmware update in some way or if the new firmware is just more sensitive to format errors on the SD card itslef but this has fixed that issue for me as far as I can tell.
A good tip is to avoid sharing SD cards between cameras too but if you do then do a full format prior to using the card in a GoPro, then also do an in camera format by going to settings delete all/format prior to use to ensure your SD card is clean and properly formatted for the GoPro.
Many devices do leave extra files on the SD card as may your computer whenever you connect your camera to it via USB, other devices may also reformat the SD card to a different format and the GoPro from my experience gets unstable with different types of formats and some left over hidden files or folders on the SD card.
I never normally connect my GoPro to the PC to transfer files but instead use a separate SD card reader, transfer speeds are much faster on a card reader and by not using the USB plug and play feature when connecting a device it avoids the computer from putting extra crap onto the SD card which has shown to sometimes cause issues with the GoPro cameras.
The only other times I had such issues is when I shared my SD card with other devices, this was fixed with the same method and that's why I tried this to see if it was the cause too which it seams as it was.
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One reason I can think that this firmware update could also be causing issues is that after the update the date setting in the camera is reset. If you have any files on the SD card from prior to updating this could cause the camera to freeze by it seeing dates that are ahead of the cameras date causing it to freeze as in the huge year "2000" bug lol.
This could be due to other video or image files on the card or any of the other hidden files or even folder creation dates on the card itself.