RSW

In Branded7e take a look at W46.

Turn 32:
Industry=10
Usable Industry=9
Metal, Mines=9(9),9
Turn 33:
Industry=10
Usable Industry=9
Metal, Mines=9(0),9
Turn 34:
Industry=10
Usable Industry=0
Metal, Mines=0(9),9

Someone forgot to bring the shovels?

I bet you have exactly 9 population on that world.

In any given turn, each population can either work the industry, or the mines. They prefer working industry if there is enough metal, but if not, they'll work the mines. This means that in a very low-population world, you end up mining on alternating turns only.

David

There is 9 population, but it looks like they've been moonlighting too...