Simple overset text problem

Hi guys! I'm currently learning to use InDesign so sorry for the noob question.

I have been inserting relatively long (20-30 pp.) docx files into a project in learning how to design a print book using a tutorial. I've been using primary text frames and all that. Now, I tried inserting a new text onto a blank page (the option to create multiple new pages when a document is inserted is on) and I get the overset text error and no new text. Additionally, I created a new page and simply wrote a sentence in it and the moment it reached the frame it disappeared, meaning that it doesn't automatically insert a line break for some reason. Maybe this is the problem with the previous text I tried to place as well.

What's weird is that I don't have this problem with the existing text - when I write something in the middle of a line it just pushes the following text to the next line.

Can you help me with this?

Cheers