These are bend-straight waveguide offsets, a common feature in photonics:
pure.tue.nl/ws/files/4294122/590296.pdf

You can either create your own interconnect without offsets:
tutorial: nazca-design.org/xsections_and_layers/,

or set demo.shallow.offset = 0, for example:

import nazca as nd
import nazca.demofab as demo

demo.shallow.strt(100).put()
demo.shallow.bend().put()

demo.shallow.offset = 0
demo.shallow.strt(100).put(0, 100)
demo.shallow.bend().put()

nd.export_gds()