WordPress Update Messed Up Custom Password Message

I had included a custom password message on my website and it was apparently overridden when I installed the most recent WordPress update. After that, the custom password message disappeared and has been replaced by the default one. I thought the update may have deleted or replaced the custom text message I had added to the functions.php file, but that file and the custom text is still there. I found the default message text in the new wp-includes/posttemplate.php file, but if I replace it with the custom message text, it breaks my site.

I also tried using the only custom password message plugin that seems to be available, but it hasn’t been updated in a year and no longer seems to work.

Can anyone help me with this?

[Moderator Note: No bumping. If it’s that urgent, consider hiring someone.]