The error occurred after I installed brew install ack.
Error detected while processing function nerdtree#ui_glue#invokeKeyMap[1]..76[18]..75[3]..<SNR>68_customOpenFile[1]..105[1]..121[3]..177[6]..178[17]
..13[3]..BufWinEnter Autocommands for "<buffer=3>"..function <SNR>124_MarkdownRefreshSyntax[6]..<SNR>124_MarkdownHighlightSources[31]..<SNR>124_Synt
axInclude[14]..function nerdtree#ui_glue#invokeKeyMap[1]..76[18]..75[3]..<SNR>68_customOpenFile[1]..105[1]..121[3]..177[6]..178[17]..13[3]..BufWinEn
ter Autocommands for "<buffer=3>"..function <SNR>124_MarkdownRefreshSyntax[6]..<SNR>124_MarkdownHighlightSources[31]..<SNR>124_SyntaxInclude[10]..sc
ript /usr/share/vim/vim90/syntax/vim.vim:
line 848:
E403: syntax sync: Line continuations pattern specified twice
The error occurred after I installed
brew install ack
.