Rails: "NameError, uninitialized constant" error after modifying controller code

Rails: "NameError, uninitialized constant" error after modifying
controller code

I was able recently to organize my code by grouping everything into folders.
I had an issue with having the same name for both my group of controllers
and my module under the lib/ directory but I was able to fix by following
this:
Rails: Same name for a library module and a group of controllers?
I also know that whenever you change your lib code, you need to restart
the rails server which is totally fine by me.
But after the recent re-organization, every time I change the code in the
controllers, I get the following error!!!
NameError at /admin
uninitialized constant Admin::PagerDuty
and to resolve it, I simply restart the server!!
Any advice?!