Mesh sometimes vanishes after a few dozen iterations

[ithron]

Describe the bug
Sometimes the mesh seems to vanish after a few dozen iterations (most of the cases > 60).
In those cases the Mesh collapses into a single point.
In other cases the mesh just moves (far) outside of volume bounds.
This happens within a single iteration, so the mesh moves / scales abruptly.
There is also not much visible change in the iterations before.

To Reproduce
Not easy to reproduce without an example volume (which cannot be made public).
Also depends on configuration and volume.

---

# Paths are relative the current file
referenceMesh:
  mesh:   ../ReferenceMeshes/Vertebra.off
  colorToLabelMap:
    type: custom
    map:
      - [[255, 0, 0], 1]
      - [[0, 255, 0], 0]
      - [[0, 0, 255], 3]
      - [[255, 255, 0], 2]
    undefinedLabel: 4
  origin:
    type: relative
    xyz: [0.5, 0.5, 0.5]
  scale: 1
  rotation: [-10, 0, 0]

measurementModel: ../Models/SomeModel.yml

sigmaE: 5.4
sigmaS: 1.0

maxIterations: 120
minNonDecreasing: 3
decay: 0.1

Screenshots

Desktop (please complete the following information):

• OS: Linux Mint 19 Tara x86_64
• Version: MATLAB Toolbox version 1.2.2.3 on MATLAB 2018b

[ithron]

This issue is probably related to issue #70 or #71 since after the merge of #72 and #73 it cannot be reproduced anymore.

[ithron]

Problem still not fixed.
Could be related to sigmaS going to 0 for small decay factors....