FYI Solarwinds Case: HTTP Login Page Text is not displaying correctly after Update to 15.2.3 HF2
HTML Formatted text is no longer supported in Global\Limits and Settings\Settings\HTTP Login Page Text or Domain\Limits and Settings\Settings\HTTP Login Page Text
I had HTML formatted text for my users in this location, I experimented and moved my HTML formatted text to Domain\Custom HTML\Header.htm successfully.
Solarwinds Response to My Case:
Serv-U allows using welcome messages in the Web Client feature for customers to provide more information such as how to use the Web Client, who to contact for support, and such.
This is configured in Global / Domains > Limits & Settings > Settings tab > Custom HTTP Logo, Login Page Text & Title.
On previous versions, HTML codes and tags are allowed but it was removed on version 15.2.2
Advice to use the custom HTML but we don't provide support in creating that HTML code you need to coordinate with your an internal web developer.
These are our guides for doing Custom HTML in Serv-U.