Looks like I'm not alone with my Mokka. The Vauxhall app appears to have a recurring issue where switching between deferred and instant charging becomes unreliable.
I tried restarting everything and I already updated my software but the problem doesn't go away. I'm left with no choice, I contacted my local dealer about this and have him service my car. Hope it goes well...
I suspect it had something to do with your home's electrical system. My friend, who also owns an EV, recently reported that his car stopped charging overnight due to a drop in supply in the morning.