That text does not appear anywhere within my plugin. If fact I searched for that phrase in my entire dev WordPress install and could not find it in ANY file from WordPress or all the other plugins I have installed (all my extensions and some others). So, it’s not even something that WordPress itself would output if someone tried to create an account with an existing email.
I’m guessing you have some other plugin that you use for a custom registration form for user account? I didn’t see any registration pages on your site, so that must be a non-published link. I imagine that’s the type of error message that would be shown if someone tried to create a new account using an existing email. That text must be coming from another plugin, unless you used something like my Customizer extension to modify one of the messages to say that? But, my plugins have nothing to do with account registration.
I would strongly suggest that you have one of those users who report the problem do a screen grab video showing exactly what they did to get the message. Or, at the very least, describe step by step what they did.
Or is it possible that the message they are getting is the message when they try to sign up for the same task more than once and you have not allowed duplicated signups. The default message for that is “You are already signed up for this task”, but if you use my Customizer extension, you could have changed that text (or someone else may have). That’s the only other thing I can think of that would actually come from my plugin, and is not a bug if you are not allowing duplicate signups for tasks.
Also, if you are NOT using user accounts for your volunteers then you can turn off that message that my plugin generates that says “If you have an account, it is strongly recommended that you?login before you sign up?so that you can view and edit all your signups.” Check your settings, you can disable that message by checking the checkbox for the “Disable Login Notices?” setting.
