Recently put a network extender in my home and now am almost completely unable to SEND text messages at all. I'd say roughly 80-85% of the time it fails with an error something like "nwtk fail message not sent".
1. I still get all incoming SMS messages
2. Before the extender, I had no problems texting outbound.
I have recently experienced the same thing, except it is handset related. I used to have a Samsung Galaxy Nexus and had no issue whatsoever for 2+ years sending text messages from my home with a network extender. I got a Samsung Galaxy S4 last week and since doing so have been hardly able to send any text messages.
To test the theory, I walked away from my house just far enough to get out of the range of the network extender and was able to send a text message. It also seems to be 3G/4G related. When in 4G mode with poor reception, the text messages aren't going through. When it drops back to 3G, they go through. I think Samsung should be able to fix this with a firmware update.