I’ve been working on Stud.io for the past few weeks, and while ive, done so, I’ve noticed several problems with the connectivity on the following pieces:
I’ve reported a number of connectivity issues there before, and the response time for any questions from the development team is pretty good (though you still have to wait for the next scheduled update for the part to be fixed).
As for the missing parts, you can try requesting parts there as well, but I don’t know how much they’ll be able to help.
For fan-made parts, the place I’d recommend is the DCC:
I don’t know if the project has everything, but last I checked, it’s pretty good at keeping up with the latest fan-made parts.
I’ve tried that, and it isn’t perfect. I can’t verify most stuff, but I can say that at least the gs head, furno’s swords, and the left nuparu Mahri armor piece don’t connect properly, with furno’s swords having the same connection issues and the other 2 just straight up not being able to connect properly. I have downloaded the biopack, though.