Task List won't automatically update based on Predecessors

Hello,

Apologies as I'm sure this is something that shouldn't be so hard to fix but I I've tried searching for answers before submitting this question and I can't find the solution. 

I've inherited a bunch of old projects from a previous admin and the task lists were set up manually with no template. I need to copy a lot of the projects and then adjust the tasks to new dates. The task lists are very simply and straightforward.10 tasks total and the predecessors go down 1, 2, 3, etc. starting with task #2. The issue is when I select a new completion date and adjust the start/due date for task #1 - none of the following tasks update even though they all have predecessors set. 

Not sure what I am doing wrong here or what needs to change.