Hey Prathiv,
If this is an old activity, I would validate if some changes have been made to the page since the creation of this activity.
However, as you mentioned there is dynamic content being added to this page, this pertains to The structure of the page being modified during page load (at run time). Have a look at: Troubleshooting Activities
and note: In order for Target to recognize where activity changes should be applied, avoid dynamically inserting an elements with the same class or dynamically modifying the class of any siblings.