Well, are most of the tubs reading HIGH humidity? Make sure that the substrate is dry, move the water bowl away from the heat source if close. Some people have a fan blowing at the rack to reduce humidity. If you can put more holes in the tub, try doing it to one and add a few more and see if that helps that one tub. The AcuRite thermometers are pretty good. It is reading HIGH because the humidity is probably a 100%. Is there condensation on the sides of the tub(s)?

hope this helps,

Dave