video not displaying uploaded through classic editor

hello, I am using generatepress theme for my website.

I have been using classic editor to write posts and had no problems.
However I found out that videos are not display properly as you can see below.

https://imgur.com/veQ5Lzh

Not only the videos in the article that I newly publishing, but also the videos in the articles that I have published long time ago.

https://imgur.com/jX0bsqG

There were no issues like this until I found out today.

I have tried deactivating the plugins to check if any plugin is making the issue, but issues were not solved.

However, I found out that If I publish the articles through block editor, the videos appeared normally.
Only the videos published through classic editor showed the issue.

Also, I have found that if I change the theme to twentytwentythree theme, videos appeared properly no matter what kind of editor I used.

https://i.imgur.com/OLXC4bg.png
https://i.imgur.com/7MnrQtr.png

So it seems like there is some problems between the classic editor and generatepress theme.
The classic editor works well with the other themes, though.
I must use the classic editor in my website, so please help me with this.

you can check my website below.
https://funnyissue.com/?pageid=1&mod=document&keyword=%ED%95%9C%EB%AC%B8%EC%B2%A0&uid=150#kboard-document