Random words/spaces being underlined and bolded in notes app

I do a lot of writing in my notes on the iPhone SE, and ever since the iOS 11 update, random words/letters and even spaces after periods are getting underlined and/or bolded.

for example: The dog saw a cat._The dog barked at the cat._

This is very annoying because I have to go back and fix it manually each time it happens (and the phone underlines the space between sentences every. Single. Time.) I have the shortcut where if you double tap the space bar, it places a period, and that seems to be what's causing it because if I put the period in by going into the number and punctuation keyboard, it doesn't underline the space between sentences, but again, that's annoying. And still, this doesn't solve the issue of random letters in the middle of words being bolded.

I've tried the basic stuff like turning my phone off and turning it back on, I've looked in the settings for an option to turn bolding and underlining off, and I've tried deleting the notes and starting again, but nothing has worked so far. Has anyone else had this problem and did you fix it?