See:

https://www.reddit.com/r/taxpros/comments/1216b8q/anyone_else_seeing_an_increase_in_underwithheld/

and last year, too:

https://www.reddit.com/r/taxpros/comments/u1japy/so_many_people_underwithheld_this_year/

Some employers are not even transitioned for their previous hires and are taking the heat for underwithholding. I send a notice at year end and also at this time of year to remind everyone about W4 updates, retirement and benefit plans, health plan options and other life changes that affect on-the-job provisions. When they are doing their taxes, people finally pay attention to some of these topics.