Non Covnergence on buckling simulation

Goodevening I am trying to compute a steel reservoir but I cannot find a way to make the model converge. I link it here if anyone has an idea on how I can deal with my problem. [WeTransfer - Send Large Files & Share Photos Online - Up to 2GB Free]

Some parts of the mesh are disconnected and there are not any contacts stablish between them.
Try to solve 1/4 first or a smaller part of the model to gain some experience with the software.

There are very thin parts in this model, especially that vessel. You should use shell elements in such a case. Then make sure that everything is properly connected by running a frequency analysis.

You have all the model split in different parts. You can benefit from that assigning different mesh densities and improving considerably the overall quality of the mesh.

Connections are actually fine - they are realized with tie constraints plus a few contacts. Modal analysis shows that everything holds in place.