Found dip in subfloor after installing engineered flooring

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I have just finished installing a new floating, click together, engineered wooden floor in my first floor bedroom. I had been pretty diligent to prepare the room before hand, remove any raised nails, splats of plaster etc, and check for any dips in the subfloor. I didn't notice any. The flooring was installed perpendicular to the joists. The room is part of a relatively recent extension that the previous owners had done around 9 years ago. The subfloor seems to be possibly chipboard panels.

However, after finishing the install, I have found a spot that is quite springy and creaky when walked over, so I assume this is a slight dip in the panel. There is no issues at all with the ceiling in the room directly below, so I'd say its safe to assume the joist is fine. I'd say it moves at very most 1/4 inch, but hard to tell. Luckily it's near the end of the room, so lifting will only require a few rows, rather than the whole room again (even still, a massive pain in the...). I didn't notice any issue when laying the floor at this point in the room.

What is the best way to level the subfloor underneath? Not thrilled at the thought of lifting the panel and replacing with a new one. I have found this self-leveling product which says works for wooden floors, but wondering if this is the preferred method:
https://www.screwfix.com/p/mapei-ultraplan-3240-self-levelling-compound-25kg/4959f

This is the underlay I used:
https://www.screwfix.com/p/duralay-premier-wood-laminate-flooring-underlay-3mm-10m/48485

Thanks!
 
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Pouring some kind of SLC will do nothing for the movement or springiness of what you are calling a dip.
1/4" is significant and is typically joist movement.
Or sometimes the underlayment is floating ie its not landed its edge on a joist.

A couple of heavy people standing over the dip, and attempting to re-create the movement and someone with a long level/straight edge observing any gaps - same with someone below setting a long level against the ceiling.
 
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Thanks for your reply. I don’t recall the subfloor moving in this area, or anywhere tbh. Previously there was carpet down and there was no creaking in this spot, or sense of spring. That’s what’s making me think that it’s a dip in the subfloor panels rather than the joist underneath it.
 
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Just checked using your method. The drop is at most 3/16 ths of an inch, I'd say more like 1/8th.
 
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1/8" is so insignificant - why even attempt to fill? You could actually make matters worse?
Finding the new finished floor springy and creaking might be something to do with the new click flooring - trapped debris particles or lack of expansion gaps come to mind.
 
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