2) Also check none of the following apps or apps of this nature are interfering with the Textra notification:
* IntelliRing (uncheck the box for it to manage notification volume)
* After School
* Light Manager
* Cleanmaster, check quiet notifications is OFF
* CM security
3) Check Android Settings > Sound & notification > Advanced options, ensure Less frequent notification sounds is set to Default Behaviour
4) Another app is interfering, if so, this can often be spotted by looking at the list of apps in Android Settings > Apps > Cog icon > Special access > Notification access (try turning each one off until you locate the culprit). Some users report DU Speed Booster causing an issue.
5) Finally, if you have recently upgraded from Google Play, an issue can occur with internal Android code that stops notifications working until you restart your phone. So please try this also.