a lot depends on how controlled your grow room is to find out whats causing the humidity
in my grow room the outdoor weather can play a factor for example if its raining outside the overall humidity will increase but I can control this with a de-humidifier
also what I have noticed if the plant is out of ph range she will expire more water which will increase the humidity inside your grow room, the reason for this is because she can only absorb water from your reservoir and not the food
as stupid as this sounds I do calibrate my ph meter a few times throughout the grow using ph 7.0 at a temp of 25c to make sure that im getting accurate readings and the plants are in the correct range to be growing
it might be worth checking the accuracy of your ph meter to make sure your plants are in range which could also be the reason your ec is rising, if the plants cant access the food they will only be taking on water
if everything is accurate your only soloution is to get a de-humidifier for greater grow room control although its only at certain times of the year that humidity can be a problem
anything from 40%- 60% is good for flowering