How do I get Vim to highlight matching parenthesis?

An upgrade of vim from version 6.3 to 8.0 might swap/upgrade the code file that manages this MatchParen functionality under /usr/share/vim/vim80/plugin/matchparen.vim

The function to begin investigating a vim failure for highlighting matching brackets is called: Highlight_Matching_Pair(). Do an echo and a sleep and step through the code until matchaddpos(...) runs.

set showmatch is your best bet. you can also use the % command to jump between matching parenthesis, braces, brackets, quotes, etc.

DoMatchParen

in your .vimrc file

or

:DoMatchParen

within vim itself.

Edit: This comes from the pi_paren plugin (which is a standard plugin).