Resolved Blender rigging not working as expected after importing into Unity

I was following this tutorial:

and I finally been able to rig my model as I wanted, however, there's a step where he "linked", for example, arm's bones to the main bone using the offset option.
I did the same and it didn't give me any problem, but when I was manually doing the bone to mesh part, the same dotted line that appeared on the arms and legs connected to the main bones appeared on the hands. I actually don't know why it happen, but it didn't give me any issues in Blender.

The problem appeared when I imported the rigged model to Unity, and I was unable to properly rotate the hands and forearms. Also, the mesh and the bones were separated inside of Unity.

I leave an image below with the problem in action (hierarchy and the model).

Some info for context, I'm using Unity 5.6 and Blender 2.90. The model was originally started in Maya 2019, and then imported to Blender. The model was exported to FBX.