Hey, I was trying to figure this issue out and saw it asked online but not answered so I decided to make this post once I figured it out. Sometimes when you hold shift and a spell for the indicator you can't right click to cancel it and have to awkwardly stop holding shift then right-click. This randomly happens when I play on new accounts and I didn't understand why.
In hotkeys shift+rclick is by default bound to 'Player attack move click' under the 'Player movement tab', so if you unbind/rebind this your character will no longer do anything when you right click while holding shift for the spell.
**Solution:** For "Player move click" leave Set 1 as MB2 and make Set 2 Shift+MB2, so that you can walk while holding shift to easily cancel it.