GFCI breaker trips, but GFCI outlet does not?
Figured it out. My mistake. The breaker has 3 slots and pig tail white wire. I assumed that I needed to run one more white wire and connect it to the middle slot and neutral bus, not just by the pig tail white wire. It turned out that I needed to connect only pig tail white wire to neutral bus. Unfortunately I misplaced the package for the breaker and did not read instructions prior to installing it.