I was compacting main UI elements, removing dead space and generally minimizing everything.
If I use UIBuilder to edit mainhud_player at all, in anyway - the health bars break, but if I do the same edits with Notepad, everything is fine.
(Remains 'broken' after reverting, even if I use Notepad to redo what I changed to it's previous state.)
New to all this, kind of fun but mainhud_target is giving me fits getting everything aligned.