Sometimes it happens that dupes, when delivering resources to a construction of pipes or cables and also, when delivering fertilization materials to farm tiles, that they miss a very tiny amount.
That tiny amount then never gets delivered. With cables and pipes, the solution is easy, just cancel the build and start it again but it's aggravating when it happens to a mushroom tile, which takes a while to grow...
Steps to Reproduce
It happens sporadically, no real way of reproducing it other than wait.
This issue has not been confirmed by a developer yet.