The 2 things I'm aware of that cause a cham's tongue to not stick to bugs are
1) Too little water. Even mild dehydration can affect the stickability
2) Excessive supplement dust on the feeders
The cause of the dehydration should be found and corrected.
Is the enclosure too hot?
Change to a lower wattage basking bulb.
Is the environment too low in humidity?
Increase the frequency and/or duration of mistings.
Add a dripper to allow more opportunities to drink.
Feeders should only be lightly dusted with supplements, rather than being ghostly.
You may wish to help your brother and his cham out by printing out this forum Panther caresheet, which lists proper temps and humidity, etc.
https://www.chameleonforums.com/care/caresheets/panther/
It gives good, sound directions for keeping a Panther cham healthy .
The other info in the Resources section of the forum gives plenty more info about a variety of things that all chamkeepers need to know.
Every Resources page has links to the other pages on the lefthand side.