MacOS – ZSH terminal displaying characters and cursor in the wrong place

Much of this depends on the setup you have done in ITerm and setting up shells.

By default iTerm runs the shell in /etc/passwd as a login shell. By default the shell is bash but the user has changed this to zsh

zsh has several files that are used at startup see zsh manual $ZDOTDIR is by default your home directory

Commands are first read from /etc/zshenv; this cannot be overridden. ... ...

Commands are then read from $ZDOTDIR/.zshenv. If the shell is a login shell, commands are read from /etc/zprofile and then $ZDOTDIR/.zprofile. Then, if the shell is interactive, commands are read from /etc/zshrc and then $ZDOTDIR/.zshrc. Finally, if the shell is a login shell, /etc/zlogin and $ZDOTDIR/.zlogin are read.

So when items starts a login shell (and assume no global files in /tc) the following files are sourced

/etc/zshenv
~/.zshenv
~/.zprofile
~/.zshrc
~/.zlogin

If zsh is started from a shell prompt it is not a login shell and so only the following are read

/etc/zshenv
~/.zshenv
~/.zshrc

If you get different behaviour in the two cases then look at your ~/.zprofile and ~/.zlogin .

In this case one of them probably is sourcing ~/.zshrc. Note that this differs from bash where a login shell reads ~/.bash_profile and a non login shell reads ~/.bash_profile and this the normal bash use is to source ~/.bashrc in ~/,bash_profile so to stop the need to duplicate code.

Terminal is suspending the editor because some other process is writing to the terminal.

Running stty -tostop should fix it.

If that does not fix the problem, take a look at this GitHub issue from the oh-my-zsh repository.

the issue results from a setting :set shellcmdflag=-ic. After I comment[ed] that out from .vimrc all relevant problems were solved.

Other users have evidently run into this problem. This seems to be the correct solution.