Issue with clocks running fast
Digital clocks convert the AC line voltage to DC and in most cases use a crystal oscillator but in some designs multi vibrator circuit or rc time constant circuit at many times the line voltage frequency for improved accuracy. I have seen RFI (radio frequency interference) that can screw up the internal oscillator. Power spikes &amp; drooping can cause the Power supplies that power routers to hiccup requiring reboot. You may have voltage fluctuations and or RFI problems but I have never seen frequency variations of more than + - 1Hz when measuring in the U.S. , Japan or Singapore. 
An inexpensive way to reduce electrical noise is to add an RFI filter, these require a ground to work well and they are just some basic electronics that dump higher frequencies protecting the equipment. I would purchase an inexpensive inline one to test if it works a few more on the affected clocks &amp; routers would solve the RFI problem.