Windows .exe Can't make the window bigger

[Rhsolyn]

Right, so a few of my friends get this weird issue where they launch up a modpack (Two of my friends got it with magic farm 2 and one of them got it with unleashed) and they get the default screen size (like you know when you first launch up minecraft and it gives you that small window? That size) and they can't make it bigger. Three of my friends are getting it, so I'm guessing it's a bug.

Edit: my friend says her console is full of [SEVERE] [Minecraft-Client] @post render 1286 Invalid framebuffer operation ### GL ERROR ###

Which seriously sounds like it might be it, since I launched up unleashed and didn't get that message at all.

Another edit: My friend is now saying it doesn't fully launch. It starts spamming her console with that message and then it stops responding

 

[Theripperss]

I dont know what steps they are trying but before signing into the world see if they can click the world larger. if they are ingame have them go into there inventory then try to make it bigger.

 

[Rhsolyn]

She can't launch the game at all is her problem. A few times it just stopped responding then she kept trying to launch and she says this time it closed.