Hi there,
It is related to: https://wpforo.com/community/how-to-and-troubleshooting-2/bold-text-formatting-issue/#post-6927 (second point)

In my case there could be a problem with smartphones.
I tried the theme viewer, in this case zerogravity, in 3 modes:
desktop, laptop and phone. 

The theme is 100% responsive and can adapt to any device.
My observation is that the popup window uses fixed size and is not responsive.
It was tested also with an official WordPress theme.

pic 1 - the reply screen in cellphone mode

pic 2 - the popup window

If we put it with together with @SeanB793 comments, you may find a solution to please the users even it may be a theme issue [to me it looks like a fixed size issue of the popup]

Thank you