  In the presence of spin-orbit coupling two branches of the energy spectrum of
2D electrons get shifted in the momentum space. Application of in-plane
magnetic field causes the splitting of the branches in energy. When both,
spin-orbit coupling and Zeeman splitting are present, the branches of energy
spectrum cross at certain energy. Near this energy, the Landau quantization
becomes peculiar since semiclassical trajectories, corresponding to individual
branches, get coupled. We study this coupling as a function of proximity to the
topological transition. Remarkably, the dependence on the proximity is strongly
asymmetric reflecting the specifics of the behavior of the trajectories near
the crossing. Equally remarkable, on one side of the transition, the magnitude
of coupling is an oscillating function of this proximity. These oscillations
can be interpreted in terms of the St{\"u}ckelberg interference. Scaling of
characteristic detuning with magnetic length is also unusual. This unusual
behavior cannot be captured by simply linearizing the Fermi contours near the
crossing point.
