Hello adhrael! Welcome to the Forums.
Have you unlocked Ginger Island yet? Sometime NPCs will travel there, and so they won't be present in the Valley for most of that day.
What is your current date? If it was just Spring 25th, keep in mind that's when Pam has here annual checkup at the Clinic, so she won't run the Bus.
I would suspect it would be a combination of these two things, and I wouldn't jump to the conclusion that it is one of your mods just yet, although that is definitely possible.
Hope this helps!