I thought they gave him a new engine not that long ago, then the following race the brand new engine shit itself, so the next race they reverted back to the older engine... and Renault were going to try and upgrade the spec engine to the new one.
and now yet again they are replacing the engine. Who knows, he's had that many screwups with Renault engines this year it's become a joke.
Last year in Monza he went from 16th to 4th, and apparently (just read) that RBR's thinking is Monza requires straight line speed (something Dan has complained about). They are fitting a brand new engine with latest upgrades, in hope of giving him more pace. The idea behind the early retirement is similar to what happened to Bottas (he's the first back of grid for next race). So if any other drivers have issues in P1/P2/P3/Quali, Dan will be ahead of them anyway (and with a brand new engine).