Did you have something selected at the time?
Also, search in Keyboard Shortcuts for "scale", just to make sure you haven't changed the keystroke accidentally. If it isn't already on option-command-s, try doing an Add, then type option-command-s, and you will see a message if that combination is already assigned something else.
I checked the shortcuts list and it was set correctly. I tried to delete and re-input the keystroke and it won't even read those three keys together. I ended up changing it to Ctrl+Cmd+S since that is close enough, but that is totally bizarre. What's even weirder is that other "Cmd+Opt" shortcuts work just fine.
Next thing to check would be if you have any system wide utilities that use command-option-s. I have trouble with F6 currently if Parallels is open, it switches over to Parallels instead of giving me a keyframe!
That was it. We just started using Microsoft Teams at my company and apparently when I have it open, this keystroke does not work. Strange but at least I know now. Thanks.