What kind of enclosure is it? A tank from the sound of it.

It is highly likely that 68ºF is having an negative effect on the system. It is hard to maintain correct temps under this conditions (remember hot/warm spots are one 1/3 of the temps cool side temps at the surface and the air temp matter as well.) 90ºF/80ºF and high 70s to low 80s for air temps.

Hydrofarms preform poorly in cool rooms they just don't handle the rapid changes in cool rooms well. They also do not have good accuracy, the spec's are rated to 2ºC up or down that is about 4ºF over or under correct.

My guess and it is just a best guess is that some of the issue is accuracy of the hydrofarms (why I suggested getting the thermometer probe as close as possible to the hydrofarm to check this) some of the is from the rooms temps as well and some is possibly how much substrate you have.

I don't think they will be an ahha moment where one thing will solve all the issues I think it more likely a bunch of small things are acting together.