I am modeling a concrete system under cyclic pushover in ATENA Science that relies heavily on the behavior of unbonded rebar. I am using 1D Reinforcement in ATENA to model this rebar, but after a few cycles, the stress-strain of the 1D elements start exhibiting strange behaviors:

1. While in the plastic region of the stress-strain diagram, the bar behavior inexplicably becomes elastic again, causing the stress to spike while still in the plastic region of the stress-strain curve. There seems to be no pattern of when this occurs.
2. The bars exhibit unrealistically large strain hardening effects, causing the bars to fracture prematurely

I assume that these are simply numerical issues, but I have tried using different Solvers (LU, PARDISO, etc.), stiffness types (Elastic, Tangent), no. of iterations for convergence, etc. to no avail. Are there anything else I can try to solve this problem?

Thank you