The div is too big! Random 3 pixel padding makes selecting multiple mail items a drag.
On the left side of each article of mail, there is a checkbox. A user would like to go through the list and check off a lot of checkboxes. This is possible to do. However, there is a bug in the size of the section that holds a checkbox. The checkbox is height 68 pixels. The div that holds the item is 71 pixels. This means that there is a small 3 pixel gap between each mail item. When we go through the mailbox ticking off mail checkboxes, and accidentally arrive at one of these 3 pixel gaps, your evil development crew has seen fit to unselect all the checkboxes.
Your evil developer put 3 padding at the top of every div that has this: data-test-id="icon-btn-checkbox-container" and made it so that clicking on this little gap that is within 10 pixels of the checkbox DESELECTS ALL THE CHECKBOXES. WTF.

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Tommy commented
Apparently other users have complained about this issue but provided less detail.
https://yahoo.uservoice.com/forums/600772-new-mail/suggestions/33199270-please-make-checkboxes-for-selecting-emails-larger
https://yahoo.uservoice.com/forums/600772-new-mail/suggestions/19810501-checkmark-selection-not-well-designed
https://yahoo.uservoice.com/forums/600772-new-mail/suggestions/20315683-checkbox-and-other-gui-buttons-are-with-thin-frame
https://yahoo.uservoice.com/forums/600772-new-mail/suggestions/19735678-area-around-checkboxes-should-not-open-the-email-w
https://yahoo.uservoice.com/forums/600772-new-mail/suggestions/33068953-checkbox-problems
https://yahoo.uservoice.com/forums/600772-new-mail/suggestions/19989769-selection-box-way-too-small-trying-select-multiI'm fairly sure that all these users are complaining about the same thing. There's a random 3 pixel padding that is close to the checkbox, and inadvertent clicking of this area actually interacts with something that is not the checkbox.