So, I must say, I love encountering problems like this, and I fixed it. I don't have read receipts on, but I have it for my girlfriend. The individual read receipts problem started happening when I noticed she went into a bad area with service. So, I wasn't getting her read receipts anymore on my iPhone XS Max, but I was receiving it on my MacBook via the iMessage. Her read receipts for me was turned on, and mine was turned on for her, she would see mine, and I wouldn't see hers, it would just say delivered. It bothered me for 24 hours, and turns out, it was HER phone that was the issue. So, these are the steps I did to fix it. Keep in mind, I did this for BOTH of our phones, for the **** of it, when they were side by side.
Had both phones together:
1) Signed out of iTunes on both phones
2) Signed out of iMessage on both phones
3) Went to Settings > General > Reset > Reset Network Settings (Keep in mind this will only reset network settings and Wifi passwords)
4) Force restart the phone. On iPhone XS Max and X - Quickly Press the Volume Up button > Volume down button > Then Press and hold the Power button until you see the Apple Logo.
5) Once both phones came back on, I signed back into iTunes, turned iMessage on, and it worked. I didn't have to reset the phones, although I backed up both phones, because I was about to, thank goodness I didn't have to, that would've been another few hours out of my life. But it could've just been an issue that the network settings were bad, but I did all of this for the **** of it.
Everything works fine now. After long hours, feels good to figure it out.
Thanks for Reading!