Every time I press the home button to get out of an app: meaning that the app is running in the background, then press the home button again to swipe away or close the app the message, "unfortunately the process com android systemui has stopped" , appears and I get sent to lock screen. I haven't done anything to my phone before this message kept appearing. I didn't touch any files, download games, or do anything risky to the phone. Is there a way to fix it? If there is please help.
I have the same problem as you have. It has appeared yesterday. After I have tried all the suggestions found on the internet and none got results, I came to the conclusion that this is a new issue. I reset my device to factory settings more than a few times. With the fresh installed os the problem disappeared. After syncing all the apps from google account got me to the same error. I have followed which application fresh installed got me to the same problem. I saw a relation between google application https://play.google.com/store/apps/details?id=com.google.android.googlequicksearchbox and this error. I have uninstalled it and yes that was the reason. But this is not really the solution as I don't have access to a lot of stuff without google app.
Both my wife's & my own Samsung Galaxy S3 phones displayed the same error message "unfortunately the process com android systemui has stopped" this morning, Jan. 21, 2017. Uninstalling the updates in "settings>more>application manager>google>uninstall updates" solved the problem. Also appeared on myTab 3. The problem came back after using the Chrome browser on one phone and had to repeat the uninstall. Very concerning and annoying problem!