I used to work for a Telco and our customers had tight timeframes on their service with rather significant penalties. One of their customers would see their connection go down once to twice a week for about twenty minutes at 8pm local time.
The cause was tracked down by a field tech attending site before the regular downtime and discovered the cause was the cleaner chocking the comms room door open so he could vacuum the floor. The only problem was that the power cable for the site router was directly in the way between the door and the cabinet and the door being wedged open twice a week against the cable eventually killed the cable via metal fatigue. The immediate fix was not chocking the door open hard like that. The long term fix was replacing the cable with one with a 90' connector that sent the cable straight down instead of out to be vulnerable to this.