Other than digging through the OS and AGS logs and looking at any recent Windows updates...
It certainly seems like it's not on your end. I'd guess Esri pushed a change into AGOL and you caught a bug.
But if it were me, I'd try renaming the "FIRE_CurrentYear_py" to something else just to see if its at all related. That is after all, the only exact reference from which you've got to work.
Or pull "FIRE_CurrentYear_py" out and publish again to some temp FS up on AGOL?
Yes, I realize it's not a "." and there's no reason anyone should be looking at it is a code file.
But I can come up with a number of scenarios where someone got lazy and introduced some odd bug.
If(FC-Name[-2:]) = 'py' .....
It's grasping at straws but everyone once in awhile you actually get the thread that unravels it all.
I'm curious, where's the pic of the fire on your profile?