In recognition of the fact more and more searches start on mobile devices, Google is preparing a separate mobile index which will become the primary source for all search queries. There is no live date yet, but it has been underway for a while. And it's not surprising - it was back in November 2016 that Statcounter data showed that global mobile and tablet internet traffic exceeded that of desktops. I'm sure your own career site's Google analytics show that mobile traffic has been on the increase for a while.
I expect your career site is mobile friendly - if not, you really have some work to do. But how about the actual application experience? Does it require a desktop or can people apply via a mobile device? What is the impact on your business of not having a mobile-friendly application process?
Currently Google has indexed your website based on a desktop user’s experience, taking into account only the desktop version of a website and the content within. With a mobile-first index, Google will switch this around to index and rank your website based on the content and information architecture of your mobile site as a primary view. While Google’s Gary Illyes stated at the SMX West conference in March, that they would fully launch the mobile-first index when results are “quality neutral”, some sites with substantially different mobile experiences to their desktop sites may inevitably find issues with rankings.