AZTEC solver - rapidly increasing temperatures going out of range

I am running an inj/prod well doublet in a geothermal reservoir with free gas at the top of the reservoir so using EOS7C (with 4-12 cores depending). The AZTEC solver crashes rapidly b/c the temperatures in the sink element rapidly increase from 120C initial T to 300C. This does not happen anywhere else in the model. Any idea why?

Solver 8 does not have this issue but is quite slow hence my attempt at using Solver 7.