It's possible for the game to represent mods in multiple ways depending on their underlying values but the trade site only supports one option to group various mods under which results in this limitation when searching for some mods.
We understand that this would ideally be a bit more intuitive but at least wanted to explain the reasoning behind it.
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We are currently working on distributing the prizes from Mayhem and will confirm on Twitter once the prizes have gone out and it's safe to delete your characters from the event.
We've raised this feedback with the team.
Thanks for the feedback, everyone. I don't have any updates to provide but wanted to mention that we're aware of (and will continue to monitor) the various discussion points that have come up around the Endless Delve event.