I've had the DVR think it's at 100% full a couple of times. A manual reboot (turn off, unplug, wait, plug back in) fixed it. If your DVR has this problem and is scheduled to record a new show, it will attempt to delete a recording to make room. Unfortunately, if it gets in this state, deleting a recording won't change it from 100%, so when it checks to see if it now has room for the new recording, it will realize it still doesn't have enough room and will delete another recording. And it may keep doing this until all the recordings are gone.
I may have a way to reproduce the 100% full problem. I don't have Quantum service, but I do have the new media server/client hardware. The DVR thinks it is 100% full when I watch a recorded show, delete it, and without leaving the "View Recordings" menu, watch and then delete a second show. Then the DVR shows that it is 100% full. If I leave the "View Recordings" menu between watching and deleting the 2 shows, it doesn't have that problem.
If everyone can keep an eye on the DVR capacity, they may be able to avoid losing all of their recordings. I just called Verizon and gave tech support this information. If someone else can try this and verify it, that may help solve this problem.