I always over plan things. I'll plan encounters appropriate to level. I'll plan NPCs. I'll plan dungeon themes. But I won't plan a dungeon themed encounter unless I know they're heading into that dungeon because it's where we ended the last session.
To put it another way: I never plan so specifically that a thing can't be moved to another place unless I'm positive it's coming next.
I almost bet the GM found a map they thought looked cool and is just throwing stuff at you to fight because it's faster and easier than coming up with storylines and characters with motivations. I get it, we GMs get busy with life and stuff too, but if you've been doing this for a while, there's always a reserve of characters or stories that you made but didn't use which can be pulled into the current game. With a new GM, they may not have that luxury.
All that said, the best course of action seems to be the thing you've already concluded: talk to the GM and the group. Maybe let someone else try being GM if it's just the case of the current one being busy. As others have said, running a prewritten campaign is just fine, especially in Pathfinder. Heck, you can even buy many of them as foundry modules with music, maps and handouts all ready.
We taking bets on whether or not it was done by a rival police gang? LASD is well known for their gang activity
I'm pretty good at repairing the means of production, so not to different here
I like to tell people "wow, he never does that" even when he totally does that with everyone. It makes people happy