Terminal always shows these extra lines after being opened

enable is a Bash shell builtin command that takes/expects other shell builtin commands as arguments to list, enable or disable them … You appear to have an uncommented statement/line like enable bash completion in interactive shells in one of the Bash Startup Files and that shouldn’t be there … Those startup files are sourced automatically every time an interactive shell is started (like when opening a new terminal … mainly the files ~/.bashrc and, on Ubuntu, /etc/bash.bashrc for interactive non-login shells … As well as any other files that are sourced in those files with . file or source file) and all lines in them are parsed and commands in them are executed in the current working shell unless a line is commented out by having # at its beginning … Therefore, this might happen:

$ enable bash completion in interactive shells
bash: enable: bash: not a shell builtin
bash: enable: completion: not a shell builtin
bash: enable: in: not a shell builtin
bash: enable: interactive: not a shell builtin
bash: enable: shells: not a shell builtin