MF6 transport convergence issues

[rcon...@gmail.com]

I am running an MF6 transport simulation. I am having issues with convergence. I am using the forward scheme in the ADV package and adaptive timestepping. I am using mvt, lkt, sft, and uzt but the cellids where the solver gets stuck does not seem to be related to any advanced packages.

I have attached a screenshot of the mfsim.lst solver output when it gets stuck. 

Is this type of issue indicative of a mass balance problem in the flow model? I have my flow model convergence tolerance set extremely tight (OUTER_DVCLOSE = 1e-4; INNER_DVCLOE = 1e-4 (units are meters and days)), and am getting 0% mass errors. I get the same issue with TVD, buts its even worse. 

Any suggestions?

[rcon...@gmail.com]

With some additional trial and error, I found that using the "XT3D_OFF" option in the dispersion package fixes the convergence problem and I am able to use TVD with a reasonable runtime and low mass balance error.  I am using uniform dispersivity field with the components of the dispersivity at factors of 1 (longitudinal), 0.1 (transverse horizontal), 0.01 (transverse vertical).

Does the effect of  XT3D_OFF provide any insight into what could be going wrong when XT3D is on?