According to my observations, the transfer of energy from one link to another deducts 3% energy, and the transfer of energy from a link to a creep deducts another 3%. This means that any energy transferred from one link to another and then used for anything incurs a 6% penalty (possibly quite a bit higher if the amounts are small, due to rounding). The documentation states "Remote transfer process implies 3% energy loss" and doesn't say anything about a loss for a local (adjacent) transfer.

Looks like this is fixed, thanks!

What is the range of meaningful values for heuristicWeight?

More info: as soon as I own anything in the room (even a flag), it becomes visible as normal. As soon as I don't own anything in the room, the room map disappears. Other rooms don't behave this way; is this an intended effect in some rooms? If so, is there a Room property that can distinguish this?

It seems that the pathfinding doesn't deal well with swamps near exits, at least when heuristicWeight is low (I didn't try this kind of situation before the default was changed, but specifying a high value caused the creep to avoid this issue). The issue is that the creep will move onto an exit in order to avoid a swamp. Then it will be in the wrong room, and will go to the closest exit -- which is exactly where it came from. It will keep moving back and forth between the rooms without making any progress toward the goal, when all it needs to do is move over the swamp (or use a different exit position that avoids the swamp).

Okay, I guess I'll have to create some kind of priority system to make sure that energy gets delivered to the creeps that need it most, since only one can receive it each tick.

It also doesn't account for energy in Extensions. That used to be useless without energy in the Spawn, but now you can build new creeps with energy in Extensions only.

Wait a minute... can you also not transfer energy out of a spawn more than once in a tick, even if there's plenty of energy to go around? E.g. spawn.transferEnergy(creep1), spawn.transferEnergy(creep2). Will the second creep always receive no energy?

Ok, so given tscmoo's answer, this must be a real bug in the game, and not just a problem with my script. If the transfer from the spawn to the creep was succeeding the first time, the console command wouldn't make a difference.

I found another one that I can't view: E9S4