HCA: Hermit Crab Association

So I've recently had a few molters. Amy finished several weeks ago and Rory came up about 4 days ago. They were both fine together before the molting. I washed both of them after each came up.
However, now that Rory is back up, Amy seems to be acting aggressively towards him. I keep finding her grabbing on to the back of his shell and he can't seem to get away. He moves his legs around but doesn't really get anywhere (even though they're similar in size)> She often isn't moving much but is keeping a grip on the back of his shell. When I separate them he speeds away from her and up somewhere high like on top of the fake plant.
I've been watching carefully to see if she's grabbing the opening of his shell but so far she hasn't. Is this too aggressive? Could it be a big problem?
Here is a picture of her doing it (she also found his hidey spot):

How many extra shells do you have for them? Sometimes after a molt they have to reestablish the pecking order as well. I would be worried if you see them actively trying to pinch each other with their BP's. One of mine would try to change shells on top of the shell pile and when another came along he would kick the curious crab and sent it rolling down the hill! They grab and push each other out of the way as well. As long as they have plenty of shells, space, sub, protein, and are in the correct conditions it is probably just a dominance issue, which is normal.

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Are you sure their genders aren't reversed?

There are lots of extra shells around, several at the right size for Amy. Humidity, food, everything is normal/available. So far I haven't witnessed any pinching, so that is good. So this is just normal dominance behavior?

I actually don't know what real gender Amy is heh, she's very shy so I haven't been able to check for gonopores. I just picked female. Rory though I have been able to check (when he was climbing up the side of the tank) and is male for sure. But it's possible that "she" actually is male haha

I was thinking of guarding but if Rory is for sure a male (and for sure the crab being held) then that's not it. I'd just keep a close eye on them if there's no actual pinching or attempts at stealing the other's shell.