I am using Avast Free Antivirus. have noticed now that two avastui.exe process is running. What is causing this?
What avast version are you using (latest is 12.3.2280) ?
Earlier versions of avast did have two avastui.exe processes running, if you had more than one UI window open.
I am using the latest version. (12.3.2280) Recently i have reinstalled it. I have experiminted this issue so that i had open no one window. Can I stop the one of the two processes?
Does this happen all of the time after boot even if you don’t open the UI ?
Having just reinstalled it, I just wonder if a clean reinstall also utilising the avast uninstall utility might be worth a try.
I have rebooted the machine, and now it seems good. Windows 10. Windows 10 sometimes produces oddities. 
Last time, however accidentally I have installed for testing the Norton AntiVirus on the physical machine instead of the virtual machine and it have asked to remove Avast Free that i have enabled. Anyone can to make mistakes even if IT.
No problem, to err is human, to screw up you really need a computer.
It also helps to be laying on your back.
He-he.
The problem has been occured again. After System restart, the situation is unchanged. Avast Free latest stable build, Windows 10 Pro 1703.