The finite element analysis might not converge due to several reasons usually due to some element that is not sufficiently supported and can freely move or rotate.
Finite element analysis requires slightly increasing stress-strain diagram of material models. In some cases of complicated models, e.g. with multiple contacts, the increase in divergent iterations might help with convergence. This value can be set in Code setup. Most common causes of analysis failure are singularities when the parts of a model are not connected properly and are free to move or rotate. A user is notified and should check the model for missing welds or bolts. The deformed shape is shown with the items which caused the first singularity moved 1 m so that singularity may be easily detected.
Missing welds at gusset plates leading to singularity