The official website of A Certain Scientific Railgun T (Toaru Kagaku No Railgun T) announced on Saturday that the 16th episode of the series has been delayed to July 24, 2020 (Friday) due to the effects of COVID-19 pandemic. The episode was originally supposed to air on May 29, 2020.

とある科学の超電磁砲T# 16 「天賦夢路（ドリームランカー）」はCOVID-19の影響により放送を7/24に延期する事となりました。
また延期に伴い当初6月までの放送予定でしたが9月まで延長し最後までお楽しみ頂ければと思います。
詳しくは公式HPをご覧ください。 https://t.co/apIMWIUvFB#超電磁砲T

— とあるプロジェクト公式 (@toaru_project) May 22, 2020

The second half of the anime was supposed to adapt the Dream Ranker arc from the manga. New characters and cast for the arc are

• Ryoko Kuriba : Voiced by Atsumi Tanekazi
• Shaei Miyaama: Voiced by Mayu Mineda
• Rakko Yumiya: Voiced by Sayumi Suzushiro
  

The third season has a total of 25 episodes.

Due to the postponement of the episode, the series which was supposed to wrap up its airing in June will now extend till September, the message on the official website said.

The production committee is letting the fans and cast choose the episodes to be rebroadcast as a placeholder till July 24. The rebroadcast episode will be chosen by the cast, followed by an episode which will be chosen by fans through voting. On July 17, Episode 15 of A Certain Scientific Railgun T will be rebroadcast to maintain the continuity. 

Based on the manga written by Kazuma Kamachi and illustrated by Motoi Fuyukawa, A Certain Scientific Railgun is a spinoff series to A Certain Magical Index, focusing on events surrounding the Academy City and the titular character Misaka Mikoto an esper living in the city. Nicknamed “Tokiwadai’s Railgun” Misaka is the  the third strongest of a mere seven espers who have been given the rank of Level 5. The story takes place before and during the events of A Certain Magical Index.