Can't control my humidity

Remember you are getting a reading of relative humidity. That will also go up when the air cools. When lights kick back on and the tent starts to heat up the relative humidity will go down because the temp is going up. Relative humidity: Relative humidity also measures water vapor, but RELATIVE to the temperature of the air. In other words, it is a measure of the actual amount of water vapor in the air compared to the total amount of vapor that can exist in the air at its current temperature. If you are keeping a dehumidifier outside of the tent and that air is relatively low in humidity, you should be able to lower the tent humidity by simply turning your exhaust fan up to suck in more of that air. I hope this helps.

Do you still run the extractor fan at night?? If not, that might help lower it and keep running the dehumidifiers 24/7 in the room the tent pulls air from. Also on days your water its going to be higher if you gowning in a medium vs DWC kinda thing. Good infromation listed in the other answers as well.

I almost ready to bet you water your plants around the time lights go off. Your screenshot looks like you are using controller that comes with a probe. Where exactly is your probe located? I understand that you cannot answer my questions here, but just think and see if what I am saying makes sense.

You need a bigger dehum or grow smaller plants / fewer plants -- a smaller canopy one way or another. increase in leaf mass is directly related to increase in released moisture into that room. if in a dry area, exhausting the moist air outside or otherwise isolated area from the grow area would help too. RH at night is only dangerous when the temperature drops. If your dehums cannot keep the RH a safe distance from dew point,that is almost a guaranateed tragedy of WPM. Does your temp/rh probe poll every minute or so? if so you can easily look and make sure it never spikes over that 60-65% range. If so, you are okay. If the plants are still growing larger, you'll have to keep an eye on that. The first hour or so after lights out is going to be the biggest thing to monitor, if you can. don't open a tent during dark cycle in flower phase, obviously. As long as it doesn't rest higher than 65% and you don't get a spike during the first hour, it should be fine. Plant stomatas close at night. Very little transpiration occurs. It is not optimal, but should be safe. From what i have read you don't want a VPD shift of greater than 0.4 from day to night. if your equipment is struggling to keep up with the mass of leaves (trasnpiration), then you probably have a greater swing than .4. It's not the end of the world. And, if you do correct it, you'll see the benefit is not huge or even visibly noticeable if you weren't far off before. It'll reduce risk of various issues and the pickier genetics out there that might react to such a thing while most dont. As long as you aren't growing mold, you are relatively fine.