In the real world, "slips" occur with more than half of orders.. if that is any indication.. I do not think it is a problem, it is extremely realistic.
My office was involved in retrofitting some pre-deployed vehicles with upgraded communications and situational awareness gear prior to the 2003 Iraq invasion.
We had a short lead time before our deadline, and a lag in production that ate up "normal" shipping time, so we decided on air freighting kits into the retrofit point using the military airlift command when we found out that commercial shipments were subject to the same theater transportation priorities for landing as military aircraft.
Our supply gurus said that if we used "Priority <some number I don't recall>" it notifies the shipping point that our stuff should to the front of the shipping queue and the traffic management types will decide whether it can go on military aircraft or supplemental commercial carriers to meet our schedule.
After numerous calls from our pre-deployed install team that they haven't seen the parts, and we're spending money to have them sit and wait, we got in touch with the airlift authorities.
After complaining "But, we have a priority <can't recall the number> on the parts," we got the response, "Good, so does everyone else requesting air shipment." After waiting our turn, and getting the shipment, the next delay was in cataloging and reviewing the contents of the conex containers used for the shipments.
The install job got done before our program deadline, but not without eating up our project slack, and implementing a shortened live training time with equipment installed for the troops being deployed to use the vehicles.
Like you, seeing slips in the game didn't alarm me because I was aware of slips in real life, even after I eliminated those caused by my poor battlefield planning.