Some of my family were mad because I wasn't responding to texts. I wasn't getting them.
I've noticed also if a message is over 160 characters, it will just eat the first message, and I only get the 2nd part.
Samsung Galaxy 5.
Using the Messages System that comes on the phone.
I've tried using Facebook Messenger SMS, and it seems to be working fine, but I don't like the interface.
There are only so many things you can try when you're having this problem.
Check for an update to the messaging service
If recently updated and then the problem started, uninstall the update
Check storage amount
Check for phone update
Switch to Verizon Messaging service vs. Samsung Messaging (little yellow envelope?)
The s5 is getting a little outdated. I know they stopped providing updates to the s4 and I imagine the s5 is not far behind. As a last resort I would do a factory restart. That always seemed to solve my problems with the s5 - slow camera, text not always being received, apps suddenly closing etc.