Lepidopterologist Will Not Unlock

[RhysCake]

I must have collected all 13 butterflies at least 5 times back in 2018, never getting the achievement to pop. I just did it again today after seeing this game in my library with that one achievement still keeping me from the 100%. And after doing it all again, using a guide because I'd forgotten where they all were since I last played, the achievement still didn't work!

What am I doing wrong? Is it just completely broken. I even reset all my progress on this play through. Then had to complete it once to get the golden key and then again getting all the butterflies.