I'm having an issue where if I send a campaign invite my players will be able to see a list of unassigned premade characters for it but are unable to view each character's sheet by clicking on it. I believe I was able to do this before and the arrow next to each character implies the UI was designed for this. Each character has the public view option selected. The only option that has worked has been to join with a random character and then unassign the character afterwards. Is there a setting somewhere that I'm missing?

You can just give them the character sheet share url while set to public. Then they can see the sheet. 

If they're joining and claiming a character, it should be because you, as DM, have already explained or shown them what they need to choose the character or because you made the character for them, so they already know that's who they'll be playing. 

For more about character sheet sharing here is a 2-min video:

In this case, I made 12 premade characters and was gonna let them choose from the choices for a one shot I'm doing. I did this previously and it worked great but now people are telling me that they can't view the characters individual sheets on the invite link. I can't remember if it was like that before and they had to do the workaround I explained earlier or if something changed since then. I'd rather not send each person 12 url links each. I can do the workaround for now but I wanted to know if this was intended behavior.

It has never worked that way and it is currently working as intended.

To avoid sending all the links, they can just pick one of the characters to join with then browse the others. Then they can claim the one they actually want and unassign the others. Might take some juggling between players of unassigning and claiming but should work.