UA has several rules regarding standby and Same Day Changes.
It will be helpful if you can answer:
Do you have any Elite Status with LH? If so, what is it.
Is your ticket booked through LH or UA (does it have UA ticket code 016?)
Do you belong to MP, even as a General Member?
No, I do not have any status on LH or UA. My ticket is booked through LH (ticket code 220).
Yes I belong to MP, as a General Member.