This could be one of three problems at work or a bit of all three at the same time.
1. Flour pot hole is to wide and Sprue hole to narrow to recieve the amount of glass charging the hole.
2. To much glass for the initial delivery. In some cases you should hold glass back and charge the pot up 2 - 4 times depending on glass movement.
3. Not enough time spent properly measuring the displacement of glass to fill the mold, leading to the void filling up and over flowing.
Poorly laid out Sprue or glass delivery wells so that flour pots have litle space to fit side by side on the mold if there is more than one.
Notice how I have simply used broken kiln shelving as legs for the pots to stand on. This works well yet in a situation like this if the glass is still slowlyt getting sucked down the hole it can take bits of unwanted ceramic material with it.
If you end up with this kind of a mess you can use tongs to pull the ceramic legs out of the glass puddles at temperature. Use appropriate protection and dark glasses, be quick. If you hear any clinking, close the kiln door and let it come back up to temp. before extracting anything else to save the plaster block from developing cracks.