Season 3 (season 2 in Japan) will broadcast on January 9th 2021.
The original author, Daisuke Ashihara, became ill and the original series was interrupted between 2016 and 2018. Therefore, this show was cancelled once.
Season 2 episode 1 to episode 15 (Season 1 episode 49 to episode 63 in Japan) are not in the original story, they were created by the anime staff.