Closing an app on activity log

https://www.busymac.com/busycontacts/Safe Boot from the HD, (holding Shift key down at startup), does the problem occur in Safe Mode?

Safe mode attempts to repair Disks & clears lots of caches, so if Safe Mode works try again in regular boot.

EtreCheck is a simple little app to display the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to help people help you with your Mac.

http://www.etresoft.com/etrecheck

Pastebin is a good place to paste the whole report...

https://pastebin.com/

Or use the paperclip at the bottom of a Reply to attach the full report here. :)

The process named "screencapture" is normally only running when you have typed one of the special keyboard shortcuts (command+shift+4 and others) and terminates with either the press of the "esc" key (aka escape) or by actually doing the screen shot of the screen or window or area or whatever mode you told it to do with the shortcut command.

So, you're saying that you have a "screencapture" process visible listed in the "Activity Monitor" window and you can't kill it using the normal "x" icon in the upper left corner of the Activity Monitor window with that process highlighted?

On my High Sierra system, as soon as I type a screencapture shortcut command, e.g. command+shift+4 to capture a window, I see the screencapture process appear and the screen/mouse cursor changes to a bulls-eye, and I can't do ANYTHING on the system until either the escape key is pressed on keyboard or until I actually press the space key in a desired window and then click in that window to complete the screencapture and create the screencapture file. The only possible way I can think to actually try and kill that process would be to log in remotely from another system Terminal command and manually do a "kill -9" of the screencapture process id which you could obtain from the command:

ps -axwww |grep screencapture

So some things just don't quite make sense with your description. Are you on High Sierra version of macOS? You're not talking about the "Grab.app" program in the /Applications/Utilities folder window are you? Which exact screencapture keyboard shortcut are you using? Can you post what your Activity Monitor window shows for the screencapture process info?

Good luck...