Diagnosis
Air got trapped in the water line after the filter change. It takes a while to purge all that air out, and until you do, the flow will be weak and sputtery.
How to Fix It
You need to flush the system. 1) Hold a large pitcher (at least a gallon) under the dispenser. 2) Press and hold the dispenser paddle for two full minutes. Let it run continuously, even if it's just sputtering air and dribbles. 3) Keep going. It can take 2-3 minutes of continuous dispensing to push all the air through and get a steady, strong stream. 4) Fill and dump the pitcher a few times. The flow should normalize.
If That Didn't Work
If the flow is still weak after a long purge, double-check that the new filter is installed correctly. It should twist in smoothly until it stops, and the cap should align with the arrow. An improperly seated filter can block flow. Also, ensure you removed the protective cap from the tip of the new filter—it's a common oversight.
Heads Up
Always use genuine LG filters or high-quality, certified compatible ones. Some off-brand filters have much more restrictive media that permanently reduces water flow.