If you're sure it's the last flash (it's tricky to count them) then it's the solenoid voltage.
The reset circuit gives it it's first 'brief' flicker, once it does that the reset circuit isn't even utilized.
The last flash is there because the board has found the solenoid voltage to be o.k... 42v. Your solenoid fuse might be blown, or it could be a bad connection on the mpu.