I think it def. could be the temps. A constant 88 to 90 would be better for hot side, cold side at 80. and that humidity def. needs to come up. You say screen top? Maybe cover it with a towel or something? I have limited experience with glass enclosures. what are using to heat the enclosure? If just UTH you may need to add a secondary heat source on top.

Maybe someone else can chime in here please that has experience with glass tanks.