This bug has been reported before and shares the same root issue that has been logged with Material Billboards. I’m leaving a link to the public tracker for the related JIRA UE-37381
I’m using 5.5 and this bug appears to still be here. That, or I’m seriously missing something. Scaling billboards to screen size does not work unless I set the Screen Size variable to a negative number.
As a side note, I’ve been running into a lot of similarly minor but annoying bugs lately, all of which had been reported years ago but still are not fixed. Is something wrong at Epic Games? Engine features that used to work keep breaking and not being fixed.