If the hazard lights flash when attempting to start, it's normally a sign that the BCM has entered crash mode. This is normally due to a dead or failing battery. The FL2 is extremely power hungry, so kills batteries in about 4 years, even good quality batteries fail early in them.
It's also worth checking the electrical connections to the BCM behind the fuse box, as it's not uncommon for a stray passenger's foot to dislodge one of the many connections down there.
I'm surprised the garage said there's no faults, as even a perfectly working FL2 will have dozens of codes logged.