The Eternal Fist appears bugged. It happens time and time again that it doesn’t grasp new enemies even though the killed target is absolutely killed in time and is surrounded by other enemies.
In addition, its target logic needs improvement. It would be much more logical if it grasped the enemy nearest the previously grasped target instead of targeting a random enemy often much further away and sometimes even behind you.
Yeah, I’ve seen this behaviour as well. But I found that not the duration or its mechanic of grasping another enemy is bugged but the duration element of the HUD. It seems to sometimes reset to full duration but still using the correct duration timer in the background. Then when the actual duration runs out in the background it stops while the HUD still shows some duration remaining. Could that be the issue you’re experiencing?
No. Sometimes I kill enemies witin a second or two of being grasped, and no secondary targets are being grasped even though they are right next to them.