if you have a command typed as

echo foo \
  bar

that ends up as separate entries in mcfly, rather than a single one. It looks like mcfly is incorrectly parses the history entry? The relevant snippet for that from my .zsh_history is:

: 1593624164:0;echo foo \\
 bar

It looks like mcfly is getting confused by this, and I think it only gets the last line of the command.