so far i've only encountered this with miners.

my robots, half-way through placing miners on an ore patch, suddenly stopped recognising the miners in storage. i have the alert in the bottom-right for "not enough items" showing the miner logo, and indicating the miner ghosts on the ore patch.

i have 50 miners in the nearby buffer chest (the one that spawns at the beginning of the game), and 50 in the storage chest beside the factory producing them.

i thought the issue was that my roboports connected only at the orange corners, so i placed a tight, excessive string of roboports from the chests containing miners to the ore patch. there's a large, contiguous orange area all the way. roboport area is not the issue.

so, i placed a requester chest, requested 50 miners, deleted the request, then placed a hand facing a storage chest. there is now a storage chest containing 50 miners within a few tiles of the miner ghosts, both of which are within range of the exact same roboport, which contains construction robots.

and still, the error appears that those ghost miners cannot be placed because there are no miners in storage. i have deleted and replaced the ghosts many times to no benefit.

robots will place any other object in this space. they will never place miners.

i don't have time for further testing right now.