Embedded video disappearing from posts

I am a second author for a website/blog generated by WordPress. I have the issue of not being able to embed any videos, or if I make an edit to a post that has an embedded video in it, the video disappears once the entry is updated. Can someone please help me on what is going on? The first author does not have this problem at all.
I do not have WordPress installed on my computer as I just write entries up through the website.