! Node cannot be found in the current page' warning when attempting to inspect element

Question

What could possibly be the reasons for why right-clicking and inspecting and element could result in it creating the 'warning' 'Node cannot be found in the current page.' not to mention a whole lot of headache when it comes to listeners on that element.

The odd thing about this is that it is a calendar that I imported from a Svelte code example a while back (can't find the example) and it was created with flexbox. For my purposes I had to remove all the flexbox css but still, amazingly, the date boxes don't follow typical inline-block rules, with that stupid idiotic margin that's automatically added, but actually behave in a flexbox/floated way.

I have really looked to find any reference to anything that would create this behaviour but I can't find any.

Either way, is this the reason for why clicking one of the boxes the click listener is not triggered? Mouseenter/over is recognised while mouseleave/out is not.

EDIT: Removing the mouseenter/over allows the click to work. WHY?!!!