i know you weren't asking me but i reuse soil as well, I doubt thats the issue. Are you doing no-till? or breaking up the soil between runs? Either way unless you added much more of something like EWC which retains moisture, id say this is a problem of poor drainage from the start. A whole lot of bagged soils need a bit more aeration drainage media like perlite or rice hulls or lava rocks or whatever you choose.
Also i just noticed this, you are running 2 humidifiers in your space for a couple plants? thats gonna contribute greatly to your soil retaining moisture.