So I don’t think this is related to the plugin (from my testing so far) as my function doesn’t get called until priority 30 and priority 20 is internal WP core checks the User/Pass and then passes a WP_User or WP_Error object to my plugin …
With that said, all my plugin does is check that user account for pending activation, and if it’s not pending it will return the object that was sent to my plugin …. SO with that said, it has to be something else with your site as the authentication from my plugin passes along the object it receives or discards object received and returns a new WP_Error if account is pending activation.
The only possible issue I see is the fact that I used add_action() instead of add_filter(), but really it’s the same thing, so that shouldn’t be an issue either.
Thanks for the rewrite rules, do you have Skype by chance? If so can you message me on Skype my username is “tripflex”
If not, can you send me an email here (dont want to post email address on public forum):
https://plugins.smyl.es/contact/
Few questions, what version of WordPress are you using? Is it an Apache web server?
You said it gives you a username/password is incorrect error, right? Not an error saying the account hasn’t been activated?