What might cause a mysterious networking problem?
Well if it is a wireless network interference or a weak signal might cause a network problem. Malware infections will also cause problems. Which are an infection of trojans, virus, worms, spyware, adware, freeware and grayware. Also if your router isn't working properly that would not allow the data to be transfered.
Another thing is cables can be jerked around and cause influence on the network. A firewall placed near the outside line of your network should be a good practice on your network.
I would rather have this "mysterious networking problem" better described, but I will share what crossed my mind. Because the word "mysterious" is used I assume everything seems to be in good working order and that no malware has been detected.
You want to make sure your power is "clean". Make sure that all your computers and peripherals are on circuits shared by no other equipment. Fluorescent lighting, complex sound systems, even radios, can cause signal problems within a circuit. Look for anything with a magnet, like speakers, because magnets can interfere with signals even if powered by a different circuit. This includes phones because of the speaker and microphone; both have magnets. Make sure that any such component is at least 6 inches from any network conductor. Look for that refrigerator magnet stuck to the side of a computer tower. (Stickers don't matter.)
Power conductors, such as those feeding your receptacles (outlets), should not run closer than 6 inches to signal conductors unless they are crossing at 90 degree angles. That means that if your network jacks and your receptacle jacks occupy the same wall cavity (that is the space between studs) this may be the source of your problem unless the conductors were run on opposite sides of the cavity. Opposite sides of the same stud is not sufficient distance.
Make sure all your computers and peripherals are on surge protectors.
Make sure all circuits are properly grounded. Just because you have a 3 prong receptacle doesn't mean it was wired correctly. And if you have any 3 prong cord ends with missing ground prongs, get them fixed. Proper grounding can fix a lot of signal problems.
As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.
Before you do any work yourself,
on electrical circuits, equipment or appliances,
always use a test meter to ensure the circuit is, in fact, de-energized.
IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB
SAFELY AND COMPETENTLY
REFER THIS WORK TO QUALIFIED PROFESSIONALS.