I had the same issue on my Nexus 5 with stock Kitkat 4.4 , so this may help.
- SMS Back and Restore made copy of texts on my Nexus 4
- copied backup to my Nexus 5
- restored messages, setting SMS Backa and Restore and def. SMS app when prompted, and then set Hangouts as def. app after
No text messages in Hangouts. Rebooted phone, still not text messages in Hangouts. I performed a test backup with SMS Backup and Restore, and it showed a bunch of messages being backed up, so it seems the messages WERE restored but just not showing.
I then went in Settings > Apps > All
Selected Hangouts, and cleared Cache and then Cleared all Data
I loaded Hangouts and all of a sudden, all my text messages were there.
Hope this helps, if so, don't be shy to hit that Thanks button below
Don't be shy to hit that 'Thanks' button
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