Hello,
Firstly, we have confirmed from the Test Site, the Error Notice upon writing wrong Login Username/Password appears fine: https://ibb.co/93h7sTZ
On your Site, for the Registration process there are a lot of requirements to fulfill which we don’t have right now. Could you please share a User Account Login details of your Site which we can use to check the issue.
Also, please once try deactivating all the third party Plugins on your Site. If the issue gets resolved, then reactivate them one by one to see which Plugin is causing the issue.
If somehow issue still persists, then please take complete Backup of your Site first, then provide us the WP-ADMIN Login details of your Site along with the permission to completely debug your Site which includes deactivating all the third party Plugins and removal of on-Site Customization changes too, so that we can thoroughly check this issue on your Site and assist you accordingly.
Best Regards
.
