Flasks Sometimes Not Working

I've recently had this start happening as well. I hear the flask drink sound play, but it doesn't register. Latency would make sense (Nelson, NZ, playing through US gateway, average ping about 250ms). It's only recently started happening, maybe the last few days to a week. During this time there's been no noticeable change in my network connection.

My healing flasks stopped working after I selected Val Pack in the skill tree. I refunded that point and they started working again.