Google likes to integrate many of its services so that they all function as one. While a great idea in concept, the implication can at times be disastrous. This was proven when Google integrated Google+ and YouTube together in an attempt to allow a more streamlined experience when commenting on videos. Users took to the internet to express their disdain for the move and it appears that they are doing so again, so for a different reason. Users are reporting a bug on Google Hangouts that is preventing them from merging their Google Voice/SMS messages with their Hangouts messages.
Google Hangouts came to existence in May of 2013. After being in development for a while, and going by the code name "Babel", Google finally decided that they were ready to release a direct competitor to Facebook Messenger and Apple's iMessage services. Group video chats, free messages to other Hangouts users, and a clean interface were among some of the great features that helped Hangouts reach over a billion downloads on the Play Store. An impressive feat that only 12 other apps have been able to accomplish.
There were some complains with the original app however, as Hangouts could only communicate with other Hangout users, so this greatly limited the functionality of the newborn app as there were not too many Hangout users at the time. Google quickly realized that this was acting a bottleneck for the fledgling app and they released an update a few short months later that added SMS integration to the messaging service.
Today, however, it appears that there are some rising issues with using the Hangouts app, as some users are reporting an issue that is preventing the merging of SMS messages with Hangouts. The exact nature of what is causing this error is still unknown, as Google has not divulged any concrete information. They did state though that they are working on a fix and will have it ready for release as soon as they figure out what is going on. A bit vague, so it may be a week or two before we see the update go live. If you are a Hangouts user and cannot stand clutter, you may want to consider switching to a new messaging app, at least for the time being.