YCM error. The ycmd server SHUT DOWN (restart wit...the instructions in the documentation

I ran into the same issue with Vundle and fixed it like this:
After installing cmake, I cd'd into ~.vim/bundle/YouCompleteMe and ran python install.py

Another problem that may cause that error is conda, you should run install.py from the python's system and not the conda one, to do that use

/usr/bin/python ./install.py

from the youcompleteme folder inside vim

I was also facing the same problem with vim and I am using vim-plug plugin manager. To overcome this I did this:

cd ~/.vim/plugged/youcompleteme
python3 install.py

Done !!!