Texts from Unknown address with "Message not found" in text. Samsung Galaxy S4.

I am not receiving multiple texts ever since the software update for the Samsung Galaxy S4. The texts are being sent from unknown address with the message "Message not Found." I know they are texts being sent to me because a lot of the time they are from friends who I see later and they confirm they tried to send something.

The software update has slowed down my messaging app in general (I'll type things and it won't show up for 10 seconds, messages downloading, etc), which is annoying, but actually not being able to respond to people who are trying to get in touch with me is incredibly frustrating and it's made navigating work and school a real issue. I worry that colleagues think I'm ignoring them. Does anyone have a fix for this? I've tried a soft reset, and it didn't work. I also tried making hangouts my default messaging app, and that did not work either. Please help! I would rather revert to the old software than have to deal with all this. A few more months of this and I'm going back to a flip phone.