If the armrest feels stuck in any direction, please check the following:

Inspect the guide rails
Look for visible damage, misalignment, or deformation where the armrest connects to the chair.
 
Check the mounting screws
Make sure the armrest screws are fully tightened. Loose screws can cause misalignment and jamming.
 
Clear debris from the rails
Remove any dust or debris from the guide rails. After cleaning, apply a small amount of lubricant and try adjusting again.
 
If the issue remains, please send us a short video showing the armrest movement and rail area, and our support team will assist you.