Netflix stock is on a tear. But its big challenge is making sure people keep watching.

Netflix stock (NFLX) is up a resounding 50% since the start of the year, with its shares currently trading near the high end of their 52-week range.

But don't break out the bubbly just yet: The company's next big challenge is maintaining high — and consistent — viewership levels.

Netflix recently released the latest edition of its biannual viewership report, where the streaming giant revealed subscribers watched over 94 billion hours on the platform from January to June.

Perhaps even more notably, it was the first report that allowed investors to digest the year-over-year trends in Netflix's global engagement. This comes after the streamer added more than 39 million subscribers over the 12-month period ending in June.

The majority of those subscriber gains stemmed from the continued rollout of Netflix's password-sharing crackdown, along with the introduction of its cheaper ad-supported tier. But the company itself has said engagement, or the amount of viewing hours spent on the Netflix platform, is a more important metric than the actual number of subscribers, especially as more competitors enter the space.

The problem? When analyzing the aggregate reports, year-over-year engagement on the platform was pretty much flat. It's unclear exactly why. But if this trend continues, it could have lasting consequences on the streamer's future.

"This lack of growth may be worrying for Netflix for a number of reasons," MoffettNathanson analyst Robert Fishman wrote in a look at the data last week. "For starters, if the lack of engagement growth is due to lack of real user growth, it implies that the subscriber growth we have seen has been simply improved monetization of an existing base — in other words, a de facto price increase."

According to the numbers, total platform engagement inched up to 94 billion hours from January to June, representing a mere 1% increase from the 93.5 billion hours viewed during that same time period last year. This comes despite that 39 million-plus surge in subscribers over the past year.

Meanwhile, average daily hours viewed per subscriber decreased on the platform, falling 13% year over year to 1.9 hours so far in 2024, down from the prior 2.1 hours in the year-ago period.

For its part, Netflix isn't so concerned. A company spokesperson told Yahoo Finance that engagement is healthy, even with recent headwinds from its crackdown on password sharers. The company also referenced its continued dominance in overall TV viewing, as shown by the Nielsen Gauge report.