[Tobermory]

My dear friend - I wonder whether you realise how impossible it is to answer such a question, based off just a single chart?

Things for you to think about: are your boundaries correct/physical/working as intended? Are the fields behaving physically during this period - if not, where is the error happening - find out why and you might solve your issue.

Finally - what actually are you plotting - residual for every inner iteration? If so, then the saw-tooth behaviour is normal. Try running a tutorial case for example.