There is a glaring obvious item to check first. You stated sanitizing with B-Brite. From the company website, “While it is not a sanitizer, …”
Of the issues people have weighed in on, unsanitized equipment would be the first variable I’d eliminate.
Digging deep into the archives for a topic I see, its all good info
This is a picture of my attempt at fermentation control. Since this photo I have simplified the set up to be for FV only. The picture was the original which was used to cool wort before FV. That setup was ineffective to cool wort quickly so now I use it for fermenting only. I built the insulating jacket from some material someone left at our storage facility. I lined the jacket with hose and used metal tape to secure the 15 ft of hose so that the whole FV receives cooling. I dropped an aquarium heater into the water to raise the FV temp at the end of fermentation.
The “also abandoned” old water cooler worked too well with the RV glycol. Once the coolant got close to 32F it foamed too much to circulate well. I switched to water with some rubbing alcohol and that works fine. The temperature controller came from Northern Brewer and included the pump. The sensor wire goes into a tube that comes with the kit so you are measuring the temperature at the center of the FV.
You could use any kind of cooling system. I am thinking about using an old Fermonster full of water (7 gal I think) inverted like the original water bottles to make a larger “cold sink” instead of just the 1 gallon built in water tub and water in the lines. That should be more efficient cooling, enough for the hot wort perhaps.
https://share.icloud.com/photos/0Huqu6uwJxVTD6mi2k1HXw4nw This is the original setup.
https://share.icloud.com/photos/05DINzhVS7j_GavoscxU6ZVjw This is the jacket
Huh… guess I should pay more attention to the dates on these. 
It’s not a problem, I didn’t catch it until the end
When I saw Gordon’s picture I finally looked at the dates.
It’s an oldie, but a goodie.
Paul