Keyboard and Mouse start behaving oddly. I've had to restart my Mac to fix this
The symptoms you are describing point to a stuck key which is plaguing the new 2016 through 2018 MacBooks and MacBook Pros with the new keyboard.  My guess is that one of the Shift keys may be (becoming) stuck.


Text in all caps
Text being selected as you move your mouse
New Tab/Windows opening when you click a link


Try using an external keyboard - this will confirm if the problem is the built in keyboard or not.  If the problem goes away, the keyboard needs to be replaced. 

Update (from comments below):  Since you're using an external keyboard, it's entirely possible that that keyboard is having issues.  Try using KeyCodes (free app) to see what keys are being pressed.  If a key is stuck, it will show up in this event viewer.