wax mine a few times a year really good and do random touch ups as I notice dry spots or if it shows signs of wear. I run it liberally from loop to loop even on serving...and then rub with leather to heat it up and work into fibers. I dont do it every time I shoot...but about every two months on the bow I am hunting with at the moment.
never had string break on me in 23 years....usually replace every 3-5 years but I switch between 3-4 regular bows for each season.
if in doubt...wax it up....shoot it and see if it gets worse...if not then dont worry and if you cant see individual strings. If you can see strings coming apart....replace it now as it may have been cut or been up against something abrasive. I guess it is just an area without as much wax on it. Shoot it in....get it set for good arrow flight. Then buy and do the same to a new string...put the original in baggy, label for bow name and such....and save as backup as it is shot in and stretched and all is good.
Then leave the new string on all the time....gives you peace of mind...and ensures a good back up string if the unfortunate ever happens while afield.