ctrl + shift + arrow up/down not working

I had this problem for a full week, where control+shift+down arrow wouldn't work anywhere (Excel, Word, etc), but if you change the arrow to left, right or up, it would work as intended.

I read in a forum that the Youtube Music App had stolen that shortcut for a user, and disabling it fixed the problem, so I tried closing one by one the programs that launch on the background on startup, and surprise surprise, the Razer Cortex app had a shortcut using control+shift+down for starting a timer. I disabled that shortcut directly on the app, and that fixed everything in Excel and Word.

My recommendation is that you start closing one by one the programs running in the background, and checking when your shortcut starts working again. 

Hope it helps!  edgarsicat