I suspect that in this peculiar case, as soon as a worker goes up and exits the tunnel to report completion of his/her workload, the repairs are in fact already

I suspect that in this peculiar case, as soon as a worker goes up and exits the tunnel to report completion of his/her workload, the repairs are in fact already behind schedule. To the foreman on the surface it's quite obvious that only a few moments have passed so how could he possibly have completed the repairs in such a timeframe. Instead the worker is merely wasting time ascending and descending into the tunnel, falling further behind schedule. So the foreman goes down to check the progress of works and of course finds them complete, because the workers have been working hard for days and days in the tunnel. And upon exiting the tunnel the foreman checks the plans and finds once again that the project is falling further behind schedule. And the workers are beyond tired from continuously ascending and descending into the tunnel all day and night, so of course the tunnel repairs fall further behind schedule. A more probable explanation might be obtained by searching for a carbon monoxide leak or other poison-induced mind altered state of working in the tunnel. Of course once you return to the surface from investigating the results taken will be invalid as you've only been gone a moment so how could that reading possibly have been accurate.