inserters are stuck in "Waiting for source items" when circuit conditions change the inserter from "disabled" to "enabled" and belt items are stationary.
moving the items "fixes the issue"
Inserter not seeing the items after conditions changing it from "disabled" to "enabled". The circuit logic is for the inserter to be "disabled" when the contents of the container it's inserting into is higher than the station average for that item. It was switched in this case due to bots removing items from the buffer chest it's inserting into
This is fixed by "refreshing" the contents of the belt:
Pure Conjecture as to cause:
A: I am dumb and this is due to me being dumb
C: ...aliens