I think you should start feeding inside your tank. Istead of taking them out to feed. Since you have no substrate there is no reason to remove them. Problem being, stress, handeling, and boredom. Frogs like to hunt, period.
I actually do feed these guys inside the vivarium, Bruce Campbell is the only one I feed outside because he can't see well.
0.0.2 Litoria caerulea
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"The gallows are no place for the stubborn//Just you and your lover as a dark souvenir" - Bad Books, Pytor