Weekly Shonen Jump has released an official statement announcing that Yoshihiro Togashi is suffering from health problems once again, which is causing the weekly publication schedule of the Hunter x Hunter manga to cease. A return date for the manga has yet to be announced.
From Weekly Shonen Jump's statement:
"Thank you for reading Hunter x Hunter. As for the publication of the manga, Chapter 401, and after, we have discussed with Togashi about his health condition, and as a result, we have decided to publish Hunter x Hunter in a format other than weekly serialization."
"Togashi-Sensei will continue to write the following chapters, and the editorial department will continue to support him until the completion of the manga. Specific publication dates and methods will be announced in future issues of Weekly Shonen Jump. Thank you for your continued support of Hunter x Hunter."
Prior to the manga's return to Weekly Shonen Jump on October 23, 2022, Hunter x Hunter had been on hiatus since November 2018 due to Yoshihiro Togashi's health. The manga returned from a previous hiatus in September 2018 after going on hiatus in April 2018. The manga previously went on hiatus in September 2017, and Togashi announced at the time that he planned to resume the series before the end of the year. The manga then resumed in January 2018. The manga had gone on other numerous hiatuses prior to these.
Togashi launched Hunter x Hunter in Shueisha's Weekly Shonen Jump magazine in 1998. VIZ Media is publishing the manga in English.
Source: ComicBook.com