The leap second was scheduled in January. That event is so unusual you might get worried. So you do a simple google search and find out that there was a critical bug[1] in Linux kernel last time leap second was inserted. People got worried rightfully[2][3]. I don't know about debian, if it was known prior, if it is the same bug as before, ... But I don't run Debian, you do.
Even if I had googled (which I didn't) then I'd probably have assumed the fixes for bugs from 2009 to have long made it into the current distro kernels.
I just didn't expect something so basic to be still (or again) broken.
Don't get me wrong, I wouldn't too by default. But do you remember Azure crashing on February 29th? And checking for that date is a matter of three conditions. Leap second is much more complex. I'm not trying to be a smart-ass.. I'm just saying it's something I would worry about and would try to find something about it. And perhaps it wouldn't lead anywhere with Debian.
And still, something in your app stack could crash on this as well, leaving the kernel patching pointless.
Almost all of my machines run the Debian stable kernel and were still affected.