Can't enter commands into minecraft server on ubuntu after re log back in on putty using screen -r?

Can't enter commands into minecraft server on ubuntu after re log back in on putty using screen -r?
Added (1). I have a minecraft server running on an ubuntu server. When I start the minecraft server I do it on a screen called "Minecraft server". When I close putty and open it again, I type screen -r and the server log appears and I can enter text and see live logs but I cant enter commands. Any ideas?

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