Slightly different results when rerunning the same PLAXIS model

Hi,

I encountered a problem during the data extraction process:

If I rerun a model without any changes, sometimes I will encounter a convergence issue at a phase where no convergence issue occurs the first time I run the model. It can be resolved by turning off arc-length control (which is not abnormal for my model, I had to do it at several phases), but the final results will inevitably be slightly different. Despite the difference is small, it does make one feel a bit uncertain about the results. Is it a known issue and can someone please provide some explanations?

Many thanks,