“LockApp.exe” is one of those hidden tasks that you don’t initially see unless you run the Windows Task Manager. The Windows Club (follow the source link below) will educate you on “LockApp.exe” and will provide steps to disable it. When I see “exe’s” such as this running; especially with a name like “LockApp.exe” I become very skeptical as to what it is actuall for and whether or not it is not a malware payload.
Its an official application from Microsoft, and is part of the default lock screen app on Windows. It’s safe. It is usually located under Windows > SystemApps > Microsoft.LockApp_XXXXXX> LockApp.exe. It is possible that this could be doing a lot more than that including notifying you about an update when you unlock your PC.