Masaki Nishina who had played Ryu Aihara / Ultraman Hikari in Ultraman Mebius had called up his co-star Shunji Igarashi / Ultraman Mebius for a video for his YouTube channel. They had talked about three topics that caused problems during the filming.
Episode 1's Balloon Scene - It seems Shunji Igarashi had to redo the first scene of the episode multiple times as he couldn't smile properly. Every time he tries, it ends being evil smile that a gentle one. He laughs saying that he made the girl say "Thank You" multiple times because of that scene.
Allergy - Shunji Igarashi had allergy and couldn't get near the animals. Well there was a scene (in episode 1) where he hugs a rabbit. While doing that scene he had did while holding his breath. Well of course, he had taken medicine before holding the rabbit.
In Episode 46, where Dan Moroboshi (Ultraseven) appears before Mirai Hibino on a horse. The original scene consisted of Mirai touching the horse. But manager told the staff about Shunji's animal allergy and they had alter the scene a bit. This scene was filmed with Shunji trying to keep a little distance from the horse.
Up until Ultraman Mebius, it seemed like it was normal for Ultraman lead actors to be dropped into river for a scene and also getting hanged into air. But only in case Ultraman Mebius, Shunji didn't do it. Instead Masaki Nishina was made to hang in air. That's also thrice.
(Shunji's left eye after the surgery / scene from Episode 38)
Shunji Igarashi had to stop the filming for one point during the filming of Episode 37 as he got stye on his eye. He had to get the surgery on the cure it. So during that time, the staff the filmed the scenes where Shunji didn't appear and once he returned back they filmed the scenes where he has to appear.
By the way, I revisited Episode 37 and it is the episode where Mebius gets turned into statue by Jashrine. I wonder if they altered the plot to transforming into statue because of Shunji's eye problem.
In the end, Masaki Nishina had asked Shunji if he gets Ultraman offer once again, will he appear? For this Shunji jokingly counter questioned Masaki Nishina if fans would like to see him as Ultraman. Masaki jokingly said, if he could lose weight, or if he wanted he could appear in the current weight gained situation as Ultraman.