Something that bit me the other day, which might be applicable here...
I was using an SMC-3 (not SMC-Flex, but similar) on a 22kW motor. During dry testing, I wanted to test the sequence without actually running any motors, so we had the motor local isolators off while we test ran the equipment.
If I had the SMC-3 set such that it's auxiliary output was set to it's default "running and healthy" output, everything operated normally. Apply power to start input, auxiliary contact closes, and after a few seconds, the internal bypass contactor comes in.
If, however, I had the SMC-3 set such that it's auxiliary output was set to "at speed", the internal bypass contactor would never come in, and the auxiliary contact would never close.
I phoned tech support, who were able to replicate my issue, and said that if they connected a motor, the starter operated normally - but without a motor connected, it behaved exactly as I described.
I cannot for the life of me work out why changing the function of an auxiliary contact should alter the operation of the internal bypass contactor, but apparently it does. The good news is, I'm absolutely certain that my "fail to start" logic in the PLC functions flawlessly.
The long and short of all this is, if you don't connect a motor to an SMC-3 and set the auxiliary output to "at speed", your bypass contactor will never come in.
It is within the realm of possibility that if you had an extremely undersized motor connected to the SMC-3, it might behave the same way.
And it is also probably within the realm of possibility that the SMC-Flex might display the same behaviour.
By the sounds of it, your motor is not so undersized that you're likely to encounter this one way or the other. But worth knowing about!