I decided to make a compilation of clips of the seiyuus being chaotic at MHA events this time :) Please note that I am by no means fluent in Japanese, so the subtitles may not be 100% accurate.

Sources (in the order that they appear):
Season 3 Line live    • [ENG SUB] 180407 My Hero Academia LIN...  
Jump Festa 2018
Two Heroes Press Conference 1    • 岡本信彦は心が無いです…三宅健太 山下大輝 佐倉綾音 梶裕貴志田未来 生瀬勝久  
Two Heroes Press Conference 2    • 【生中継!】ヒロアカ劇場版公開記念メインキャストがプルスウルトラ特番  
5 Year Anniversary Live Stream    • Video  
HeroFes 2020
Hero Day 2021 Live Stream    • Video  
Team Fatgum Press Conference
Season 4 Live Stream
World Heroes Mission Live Stream    • Video  
Two Heroes Livestream    • 【生中継!】ヒロアカ劇場版公開記念メインキャストがプルスウルトラ特番  

If you'd like to follow me on Twitter, my account is @orchid4hire. I don't really post anything, but it's the best place to reach me directly :)