Convergence and time step solver

Hi all,
How's everyone? :D

Anyway,
Just want to know, what does that curvy distorted line at the end of the diagram shows?
Does it mean I have instability convergence? too large time step?

how do I solve this? I am getting singularity error everytime.

I followed "singularity.error" on the discussion forum and the comsol employee at the end of the discussion

Regards,
Badri