Almost totally sure that the problem is too many negative eigenvalues in the tensor.  An analysis showed that around 8% of the eigenvalues of the tensor are negative (using tensor MouseTensorNyFiles, from Nyoman's data). 

Will check the other tensors and think on how to fix it.

 

Isotropic case for mouse brain did not yield any answers, although some tumours grew better especially when the number of time steps was increased. Tumours still stopped growing and concentration dropped to zero or negative.The upper video is of one of the best tumours, will run with same parameters to see if it can become any bigger.

A good example of an instability.   Will check data around this time that instability appears.