I've been replaying Command & Conquer: Tiberian Sun (with the Firestorm Expansion), working my way through the NOD campaign first. In missions where I have to build a base, after building a Tiberium Refinery and War Factory, I will build a second Harvester to harvest more remote or valuable Tiberium patches.
There will be occasions where one full Harvester returns to base and parks behind the Refinery. The second Harvester will arrive at the Refinery and drop off its load first. I assume this is some kind of queue system, where even if the more distant Harvester fills up first, it calls 'dibs' on being first to unload its harvest. This behaviour I recall from playing the game before and it's not too problematic.
If I have three or more Harvesters (and one time it happened with only two) operating out of one Refinery, without manually highlighting or commanding any Harvesters, they will sometimes gather at the base and stop altogether. One may sit still in the Tiberium field and the other two sit idle at the base. They only 'wake up' if I command them to return to the Tiberium field or choose each Harvester manually to stop in at the Refinery. During these times, I have not ordered or selected any Harvesters, nor are the Silos / Refineries completely full. There is also ample space around the Refinery for each vehicle to wait their turn.
Is there a way to prevent the Harvesters from going idle in this situation? Is it a bug or possible oversight on my part? Should multiple Refineries instead be constructed to prevent this?
There are 3 possible reasons:
When there is no more tiberium left for harvesting, the harvester will shutdown and it won't restart harvesting even after more tiberium is grown.
When your refinery is full of tiberium and you aren't building enough to deplete the tiberium, all of your harvesters will sometimes stop entirely.
Some maps have glitches in the cliffs and slopes that break unit path-finding. Most of those cliffs are fixed on the Cncnet multiplayer maps, but I don't think anyone has ever gone back to fix the missions. (Have you checked out the project called "Tiberian Sun Client"?)
Tips you didn't ask for: If the tiberium is extremely close you should have 2 harvesters per refinery. And you will need 4 harvesters and 2 refineries to be able to build efficiently. (If the tiberium is far away from the refineries then you can have more harvesters per refinery)
Harvesters cost 1400, refineries cost 2000 + a free harvester. Refineries refund 1000 when you sell them, you can do the math.