I like the wet towel idea!
That idea could be good for more than one thing too. Its possible they might like the moisture just for itself, and for cooling. And this is the first time I've heard of it, despite a lot of looking at other research by others.
I'm not an expert, but some people say if they are robbing you can see the bees fighting in front of the entrance? What does the entrance look like? And when people describe robbing they say you can see capped honey 'TORN open'. Also, it may not be so much the treatment that may have caused the robbing, but how long the hive was open that may have caused it, if this is the issue. (This one Canadian guy's youtube beek channel he states a rule of never going past a certain number of minutes for keeping the hives open past X.) (But I don't know if he's right or wrong about the x minutes; but his hives are nice and he's quoting about 30 or 35 minutes for how long to limit how long the hive is open.)
I'd probably space out the second treatment a few days because of the hive being disturbed so recently.
Also here's an idea for you to think about...
In Saudi Arabia they found that a bunch of our soldiers were getting sick. For a long time they couldn't tell why. Then they found out that soda pop acts completely different when it gets really hot. (And possibly maybe hot enough some of the plastic particles get in the soda?) Who knows. But this was what was making people sick over there. They found out that even though we thought soda pop wasn't harmful to us, it could act differently in high heat.
So, why I'm bringing this up, I wonder if you need to be careful about using the oxalyc acid treatments in the hive for certain temperature ranges, by that same principle (and for the brood especially)? (Humans think they know everything you know? And then we figure out we really don't.)
This one guy who does observational hive videos has shown that the lower the temperature the less active the bees are. In one of his videos he even shows that there's certain temperatures where the bees won't fly at all but wasps still can. Because of this idea maybe when you do this, if you chose the lowest temperature of the day to do the treatment also might help to not provoke a reaction...sometime after sun up (but not at night)?