Happened on two devices so far, one very old (so I thought it just failed from old age) but now also with a brand new one fresh from the box.
I have configured it by importing an .rsc file which includes:
/system routerboard settings
set auto-upgrade=yes cpu-frequency=500MHz protected-routerboot=enabled
(lowest cpu frequency because it’s just a station and the AP with many such stations connected is the bottleneck anyway, so why not save a little power in the hope the device and power supply will last a little longer) but then noticed the config was for the wrong SSID, so I wanted to load another one (not possible over the Ethernet port as it is configured as access port of the PPPoE VLAN, management VLAN is only over wireless), so I decided to reset it and start again.
No reformat-hold-time specified so default was 20 seconds. After reset (holding the button long enough, LED blinking 1 second on / 1 second off) and releasing the button, device reboots and is bricked. Power, User and two highest signal level LEDs are on immediately on power up, no matter if button pressed or not. Ethernet link down - no way to netinstall.
I probably still can RMA the new device, but if there was a way to recover from this state, perhaps the old one could be recovered too?
Is this a known issue with protected-routerboot that it can brick some devices permanently?
Or is this a protection feature against brute-forcing the button hold time, one wrong guess and device bricked permanently?
(I’m the owner of the devices, but can’t rule out the possibility I have released the button too soon by accident).