Crush on SetBoneWeights() 2019.3.0a11

I have this code:

Code (CSharp):

1. public void LoadMesh()
2.     {
3.         _mesh = Instantiate(_meshRenderer.sharedMesh);
4.         _meshRenderer.sharedMesh = _mesh;
5.         _mesh.GetVertices(vertices);
6.         _mesh.GetColors(colors);
7.         _mesh.GetUVs(0, uvs);
8.         _mesh.GetBindposes(bindposes);
9.         weights.AddRange(_mesh.GetAllBoneWeights());
10.         bonesPerVertex.AddRange(_mesh.GetBonesPerVertex().ToArray());
11.         bones.AddRange(_meshRenderer.bones);
12.     }

Code (CSharp):

1. private void UpdateMesh()
2.     {
3.         _mesh.SetBoneWeights(new NativeArray<byte>(bonesPerVertex.ToArray(), Allocator.Temp), new NativeArray<BoneWeight1>(weights.ToArray(), Allocator.Temp)); //SetBoneWeights(weights);
4.         _meshRenderer.bones = bones.ToArray();
5.         _mesh.bindposes = bindposes.ToArray();
6.     }

It all works fine until I run this in between:

Code (CSharp):

1. private void BindVertices()
2.     {
3.         var vertices = _skinnedMesh.vertices;
4.         var softness = _skinnedMesh.softness;
5.         var weights = _skinnedMesh.weights;
6.         var newWeights = new List<BoneWeight1>(vertices.Count * 2);
7.         var bonesPerVertex = _skinnedMesh.bonesPerVertex;
8.         var currentWeightIndex = 0;
9.         for (int i = 0; i < vertices.Count; i++)
10.         {
11.             var existingWeightsCount = bonesPerVertex[i];
12.             for (int ii = 0; ii < existingWeightsCount; ii++)
13.             {
14.                 newWeights.Add(weights[currentWeightIndex]);
15.                 currentWeightIndex++;
16.             }
17.             var vertexSoftness = softness[i];
18.             if (vertexSoftness > 0)
19.             {
20.                 var vertex = vertices[i];
21.                 for (int ii = 0; ii < _softColliders.Count; ii++)
22.                 {
23.                     var bonePosition = positions[ii];
24.                     var distance = Vector3.Distance(vertex, bonePosition);
25.                     var bindDistance = vertexBindDistance * sizes[ii];
26.                     if (distance < bindDistance)
27.                     {
28.                         var weight = new BoneWeight1();
29.                         weight.boneIndex = boneIndexes[ii];
30.                         var t = distance / bindDistance;
31.                         weight.weight = 0.1f;//Mathf.Lerp(0f, 2f, t);
32.                         newWeights.Add(weight);
33.                         bonesPerVertex[i]++;
34.                     }
35.                 }
36.             }
37.         }
38.         _skinnedMesh.weights = newWeights;
39.     }

Then it crashes every time on _mesh.SetBoneWeights() call.

Also project no longer loads. Unity process is launched but no window.

I am also normalizing the weights since they are not 1 per vertex after BindVertices().

Code (CSharp):

1.     private void NormalizeWeights()
2.     {
3.         for (int i = 0, weightIndex = 0; i < bonesPerVertex.Count; i++)
4.         {
5.             var boneCount = bonesPerVertex[i];
6.             if (boneCount > 1)
7.             {
8.                 var totalWeight = 0f;
9.                 for (int ii = weightIndex; ii < boneCount; ii++)
10.                 {
11.                     totalWeight += weights[weightIndex + ii].weight;
12.                 }
13.                 float multiplyer = 1 / totalWeight;
14.                 for (int ii = weightIndex; ii < boneCount; ii++)
15.                 {
16.                     var weight = weights[weightIndex + ii];
17.                     weight.weight *= multiplyer;
18.                     weights[weightIndex + ii] = weight;
19.                 }
20.                 weightIndex += boneCount;
21.             }
22.         }
23.     }

P.S. The project is totally broken it seems. I will try everything in stable 2019.2

So I can't make a bug report rn.

EDIT: restored the project, made a report, linked to this page.