Yup this is a known problem with Gorilla Arms, that they can be a downside if the thrown gems get blocked by others. But I'm not entirely sure how to fix it yet. I keep increasing its throwing velocity, but I don't want to do something like disabling thrown ore collisions. Checking if runner is buried in ore before throwing is also not an easy solution. The best solution is probably to just prevent situations where the entire field is buried in thousands of gems. At that stage even the mountain's ore sucking system can't upkeep with your production. Will have to tweak that further and hopefully as I mentioned in the comment above, all the new units will also help.