there seem to be rounding errors or other errors with the fuel :-(
my factory just stopped production because there were no more copper plates. my inspection showed that the requester for copper ore with 2 drones had 49.9 fuel and thus couldn't send any drones to get more copper. but shouldn't the requester have ordered more fuel to have have at least 2x50=100 fuel for two drones ?
checking supplies showed that the fuel depot had one drone waiting to do fuel deliveries and 1.8k in its storage, and the copper ore provider was full (limited to 10 stacks = 500 ore). both should be enough !?
adding more drones (to force getting more fuel) didn't help, but i (temporarily) could fix this problem by setting the request to copper ore again. this cleared the drones and the fuel from the requester, and after adding back two drones, the fuel drone immediately delivered 500 fuel and then the copper ore drones immediately started filling the requester ... why (what went wrong in the first place) ? and when will it happen again ?
edit: after reloading the old save from before the fix, the problem was still there, and i could even see exactly the same problem on a second requester which was stalled with 2 drones (waiting to get coal) and 49.9 fuel ...
should i upload that savefile somewhere ?