TOUGH3-EOS7C failed to converge after 10 years

Hello,

I am simulating an injector and producer doublet in a gas reservoir with TOUGH3-EOS7C. It runs well for the first few years and then struggles to converge with very small time steps (screenshot below).

I looked into the OUTPUT file and did not find any error message. The program struggles to converge mainly on two cells (indicated by the black cross in the screenshot below). But the variables at these two locations look good to me. I do have local refinement as small as 1m by 1m surrounding the wells. My injection rate and production rate are both 30 kg/s. 

  I plotted the pressure change at both injector and producer 

Can anyone please point me what could be the problem or what else I need to check? Thank you for any suggestions. 

Regards,

Haiyan