Minecraft 1.12.2
Forge 14.23.5.2855
Extreme Reactors 1.12.2-0.4.5.68

I have a 7x7x3 (9x9x5 shell) active reactor. The case should be around 640C with reactivity about 500%, outputting just under 8100 mB steam. The case is 238C with reactivity about 450% and is only producing ~2050 mB steam.

This is a Big Reactors design but I have used it in the past to spin 4 turbines and it seemed to work normally, creating around 20k rf/tick per turbine. The last mod update for 1.12.2 was in Feb 2021 so it's been the same mod version as before. The configuration is default. Any idea what has changed or why this is happening?