Post a pic and maybe someone will notice something that might be lowering the humidity.
I mist three times for 16 seconds over a 24 hour peroid and keep above 90 percent.
If well planted, moist substrate, and covered to not allow the humidity to escape, something is keeping it down. Also, what humidity gauge are you using? Some are not really reliable and where are you checking humidity at... low, mid or high in the viv?