Hello I am facing exactly (!) the same problem. I am using a "DE2-115" board together with the "Quartus 18.1.1 Build 646 SJ Lite Edition" on a "Win8.1prof" installation.
Has a solution to this been found in the meantime?
Actually I tried with Q16.1, Q18.0 & Q18.1 Lite that too different-different machines but I haven`t come across the issue you are facing.
Could you please help me to check at your end with different machine?
I will also check in parallel with Q19.1 Lite, if possible you can also check with latest version.
It seems that "clearbox.exe" issue is with your specific machine and it might be due to Quartus temporary files so I would suggest you to take backup first & then remove the below suggested files,
Must take backup of all files first & keep it at different place/device
Perform the below steps,
1.Create a backup of following files located at “C:\Users\<user name>”
2.If the problem still persists please try same with “.altera.quartus” file located in same directory.
please update me , how it works for you.