I had the same problem and one of the answers here helped me, but not because of an explanation, so I thought it might be useful to others.
Some plugins may depend on vim version and may work in version 7, but not in version 8, when you install MacVim, it may be version 8, and the vim terminal version may be 7, both will use them. vim and .vimrc to load plugins and configuration, when you open vim from the terminal, it can still work, because the plugins are dependent on vim version 7, but when you try to run MacVim, it will try to load plugins using version 8 and then it will work, the reason is that some of the answers worked because they replace the vim system, so MacVim and vim will be in the same major version, if you upgrade the previous version, you can do this to clear and then download MacVim or vim and check that everything works and then add Upaite to use plug-ins one by one, making sure that they do not violate vim. At least with this method, I found that one of the plugins does not work as expected, and its removal solved the "MacVim" problem.
In short: - move your .vim as .vim_bak - move your .vimrc as .vimrc_bak (suggested by @hai feng kao)
And test if this solves the problem, if in this case the plugin breaks your installation and you will need to activate some and find out what exactly is causing the problem.
Hope this helps others, I followed many of these recommendations without success, until I decided to update vim (terminal), and that too started to break, which was pointing me in the right direction.
Again hope this saves a few hours for some.
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