Sometimes it becomes necessary to do the up and down on the weight to overcome particular issues. So when you had dropped him 120 that time to get him to do the lure I think it was, then you were able to raise him and he retained his eagerness for it. But they can get complacent when kept at an exact weight at this stage, and it isn't natural for them. In the wild they are spending a lot of energy right now, even perhaps catching some prey here and there. They are also being supplemented by the adult probably even at this stage. Their weight though is going up and down over the course of days based on whether they score something and what the parents offer them if they don't score. So let's say in the wild he catches a lizard early in the day. Later in the morning the parents offer food, but because he's had something to eat he may not react in time and his sibling, who is more hungry, gets that small bird they offered. Later in the day the adults maybe have something to share but he was busy getting assaulted by the local crows or mynahs, so he missed dinner. The next day he is really hungry because it rained overnight, and he's ravenous. The adults are wet, so he makes attempts to catch things himself, burning off more weight. By noon he's in yarak and those Mynahs have picked on him for the last time as he takes one that is trying to beat on him. He gets an excellent feed and is much higher again the following day. This continues for the next few weeks.
So with your bird, if you need to give him a nudge in the field then that's what it takes. They are famous for having a 'yard weight' and a 'field weight'. At home they act much more hungry than when you take them to the field where they may say to you "Sorry, I lied" as they snub you from a tree or refuse your bags.
If you can get a bag again, I would set it up, in a field with enough prey that if he refuses those slips that you can walk over and slip him on this set up one. I would tie to a light creance and maybe hide it under a board or under a can or however to keep it calm until you can expose it to the open when you get about 10 feet away. If you can control the playing out of the line in such a way that the bag struggles somewhat to make any real height or distance, he should take it. Give him a very good feed on it and perhaps do not go to the field the next day, but instead the day after, when he's back to the exact weight he was again. If you can set up another as a backup and then go and work the local prey and if he makes some attempts, but fails, then head directly to the bag and do as before. That should be enough to get him on track. Then you just have to find slips that will provide him with the best opportunity.