My bad ... you are right this time He found firstly a decrease of pressure not an increase. But we don't know how the Li was ... I mean alone or with H. From wikipedia https://en.wikipedia.org/wiki/Lithium_hydride : I quote "
2 Li + H2 → 2 LiH
This reaction is especially rapid at temperatures above 600 °C. Addition of 0.001–0.003% carbon, or/and increasing temperature or/and pressure, increases the yield up to 98% at 2-hour residence time"
The reactor was at 580°C, so if it crossed the 600°C threshold, a lot of LiH is formed from Li and H. Afterwards when the temperature increase further then LIH decomposes
All replicators have to test first alone LIH to know how fast its breathes then ONLY adding powders .
As well as you should know if this behavior remains in relation with standard LIH breathing .. or not.