  Structural distortions and imperfections are a crucial aspect of materials
science, on the macroscopic scale providing strength, but also enhancing
corrosion and reducing electrical and thermal conductivity. At the nanometre
scale, multi-atom imperfections, such as atomic chains and crystalline domain
walls have conversely been proposed as a route to topological
superconductivity, whose most prominent characteristic is the emergence of
Majorana Fermions that can be used for error-free quantum computing. Here, we
shed more light on the nature of purported domain walls in Fe(Se,Te) that may
host 1D dispersing Majorana modes. We show that the displacement shift of the
atomic lattice at these line-defects results from sub-surface impurities that
warp the topmost layer(s). Using the electric field between the tip and sample,
we manage to reposition the sub-surface impurities, directly visualizing the
displacement shift and the underlying defect-free lattice. These results,
combined with observations of a completely different type of 1D defect where
superconductivity remains fully gapped, highlight the topologically trivial
nature of 1D defects in Fe(Se,Te).
