You can try editing core/classes/Input.php in a text editor, delete all code inside and replace with this new code.
Maybe try a full URL starting with https?
If it still doesn't work, there was a bug to do with local links in topics which has been fixed since the last release; I am not sure if your custom template includes the fix or not.
Thanks for the report, not too sure why this is happening.
A quick fix is to remove this line of modules/Core/pages/login.php
You can edit the template to achieve this.
If you're using Nameless v1, the template files are in the styles/templates folder, and 2 is custom/templates
Please open a support ticket over at Nameless Hosting or join their Discord server for support; this is for the NamelessMC website software only.