Factorio Forums

See selected miner in attachments - when you have a miner that is placed across 2 types of ore and the belt is backed up, you can see that the iron is depleted, however none actually comes out on the belt - it just disappears.

I am not sure if the copper is also disappearing, because there was too much of it left to see it being depleted. I presume it might be going missing also

Nothing shown here suggests a bug, you have multiple miners mining the same tiles so of course a blocked miners resources can go down. If you want to look into this further have only one miner on the patch and count the outputs.