I realized that the problem that were happens in the bolts were purely geometric. When the drawing was done in CAD and the constrains were introduced, everything seamed fine, but when the geometry is imported to ANSYS, then there is small interference between the bolts and the wholes, causing that large stress. Then, it was better to remove the small bolts and continue only with the large/main one. I will redo that geometry inside ANSYS to see if that problem still persists, but for now, with the simulation only with the main bolt in the geometry, the big stresses do not occur anymore. However, I am now facing a problem, which I am suspecting is a mesh singularity problem.