OK, this is weird. After being down overnight for about 11 hours, my blade spontaneously started working normally for about 11 hours, and it has now stopped again. 
If you have a way to log the output from your stratum mining proxy, you should check for unusual output at the moment when it stopped hashing. It should be at least a starting point to debug.
Sometimes, my stratum proxy doesn't reconnect on disconnection from pool, or takes ages before it reconnects.