I'm getting notifications every time someone replies to a topic I've posted in before. Not quoting, just random twosomes to OP. is this a glitch?

It's not a glitch, it's just how the notification system is configured right now.

A new system is going to take a while to implement, since it seems like nobody has created a competent plugin.

Okay. Also, while I'm here, when I click the + sign next to my post (mobile), the modify post and report options are invisible, you have to guess where they are.

That is literally the very next thing being fixed. We're going to put in a larger array of buttons at the bottom of each post for mobile.