Ok, I have found what was the issue. I was calling Game.getObjectById(...) before "loop" was started. The first time the method is called it seems to work, but later it seems to return old instance of the object (or some other garbage).
Maybe the method should fail when being called before "loop"?
My link has Cooldown = 0, but calling "transferEnergy" on it results in ERR_TIRED. Source link is full, target link is empty. After some time the transfer eventually happens, but it takes something like 100 ticks.
Cooldown value of link logged on each tick:
[12:19:14 PM]Tired: 13
[12:19:18 PM]Tired: 12
[12:19:22 PM]Tired: 13
[12:19:28 PM]Tired: 10
[12:19:32 PM]Tired: 10
[12:19:38 PM]Tired: 13
[12:19:42 PM]Tired: 12
[12:19:47 PM]Tired: 13
[12:19:52 PM]Tired: 10
[12:19:58 PM]Tired: 4
[12:20:01 PM]Tired: 12
[12:20:07 PM]Tired: 12
[12:20:12 PM]Tired: 12
[12:20:16 PM]Tired: 13