I lived in the building for a while and there is a bit of subtle ramp into the building but it's not quite a 1.5 foot drop because the direction (Try looking at Google Street View from before 2020 at 350 Mission St and 399 Mission St)
How was it? Did you like it there? It strikes me as soulless.
Yes this would be interesting to know. Maybe when the building sinks the sidewalk sinks as well?