Congratulations - He hit the 'honey pot'
It's funny how they find YOU

The hygrometers are very frustrating.
Use a fan ? Ventilate a little more? Move them around ?
I have never found one that is reliable.
You want to use them as a guide while you are getting comfortable making a judgement on the humidity.
Maintaining his temp is more important.

If ....or .... when you add any wood to the enclosure be sure to bake it first--- to get rid of all the nasties.
Plants should be prepped first --- bleach dipped roots and all ( 1:10) (bleach:water) then rinsed, rinsed, rinsed in de-chlorinated water.

When rinsing -- submerse the entire plant. If it's a delicate plant re-pot it into ABG / spray it often / and wait several weeks to 'grow it out' before planting it into the frogs's enclosure.