Looks like neither Super + Page Up / Page Down nor Ctrl + Alt + Up / Down work to navigate between workspaces. Have they changed the key combinations yet again? 
Super + Page Up/Down works for me FWIW and I didn’t touched that keybinding. What distro are you on?
Arch Linux. (Ignore the following: just to fill up the 20 chars quota.)
I’m also on Arch Linux. Super+PgUp/PgDn works to navigate between workspaces, as does Ctrl+Alt+Left/Right.
Check in Settings > Keyboard > View and Customize Shortcuts > Navigation what the “Switch to workspace on the left/right” are set to.