I like the way that you solved that problem, especially the way that you discovered what the problem was. So many people try to solve the wrong problem.
As a software developer, I always worked 8 hours and my management knew it. Hour #9 was minimally productive, and #10 to #12 introduced bugs that took up to three hors to fix the next day. So, working 4 hours overtime actually cut 3 hours of the real productive time the next day.
I was fired from my second job for that. They said in the interview that the work day was 8 hours. However, they expected us to come in at 4:00 am, test programs, go to breakfast, then work 8 hours. I left work around 1:00 pm, after 8 hours of work. I had to pay a big agency fee if I quit.