Failed to find a solution. Divergence of the linear iterations. Returned solution is not converged.

Module: AC/DC, Study: Frequency Domain

Sir/Ma'am,

I have modelled a coil which scans the surface of a sample material for any superficial cracks. For this, i have introduced a small crack and also i have modelled the coil along with a ferrite bobbin.
The coil is scanned for a distance of 50 mm in steps of 1 mm for crack detection. So during scanning exactly at the vicinity of the crack (where the bobbin meets the crack), the solution do not converge.

Mesh used: Crack, Coil and Bobbin - Extra fine and the remaining area are fine mesh.
Frequency Used: 100 Hz (Low frequency)

Solvers used: Iterative-> 1. FGMRES - In this the solution oscillates around a particular value after 50-60 iterations.
2. BiCG - The relative tolerance in the convergence plot is monotonically increasing with very huge values of the order of e15.
Direct-> MUMPS: Failed to find a solution. The relative error (8) is greater than the relative tolerance.
Returned solution is not converged.
All this happens only at the vicinity of the crack and in the other scan locations, i get a converged solution.

If the coil and bobbin size are doubled, we get a converged solution through all the sweep points.
I am attaching the mph file for your reference.

Regards,
Mahesh