WAN2 did the same thing.
Yes, I've swapped the Ethernet cable and I changed ports on the Comcast SMC cable modem.
I swapped in a spare USG100 on Friday and they've been running fine since.
When I unplugged the Ethernet cable from WAN2 after the last deadlock, the link lights stayed on.
I called ZyXEL and they issued an RMA.
I think, sadly, that I can no longer say I've never had a ZyXEL router have a hardware failure