LG G6 from Fido screenshot function not working. Workaround?

[Android Central Question]

The screenshot function used to work but now has stopped working. Any ideas on restoring this function.

 

[B. Diddy]

Welcome to Android Central! Do the Power and Vol Down buttons still work separately? It still ought to be Power and Vol Down pressed simultaneously, for about half a second. Does it work in Safe Mode? https://support.t-mobile.com/docs/DOC-34097