Thanks @ja79! The disable/enable switch worked for me. I lost a few new messages that didn't save properly since the Android update, but that's a small loss compared to a factory reset. I have notifications with my incoming SMS again!
Regarding the Sony Xperia Z3v & messaging issues relating to 5.1.1:
I had issues as well after the update and found a possible solution.
Set messaging plus as your default messaging app.
Go to application manager and reset app preferences.
Power off the phone for about 30 seconds and power up.
It should be noted that GO SMS Pro and GO Contacts EX do not work as of right now with 5.1.1.
I hope what I provided helped!
Also having issues on the new Lollipop 5.1.1 update with send and receive on and app besides Versions Message+, even with this app I have noticed when I receive a text it shows up under my notification bar for about 2 or 3 seconds than disappears and when I go to the Message+ app it doesn't show any new messages like it used to, with the red circle and number of new messages inside.
I am using Textra Textra it is working phenomenally well and a real good MMS SMS app.
Sent from my Verizon 4G LTE Smartphone
To all, you say SMS app for Textra Textra. I've used it since installing 5.1.1 and app is phenomenal get it at the Google Play store. Again Textra. The app is for free.
Reset the phone and it will take care of all the problems with the messaging. For some reason people have had to do this to get it all to work. Backup all your stuff and then do a factory reset and you will have it all back and working. Thanks