Version 1.2020.8 is ok. In version 1.2020.9 the superscripts position vary a lot by the skinparam dpi. In the following example, using or not using dpi 300 make the difference. Example: using dpi 300, the superscript "2" is almost completely overlapped to the letter "r". (Note that the legend works only on the top because on the bottom is ovelapped to the diagram).
@startwbs
skinparam {
'dpi 300
legendfontsize 12
shadowing false
titlefontsize 12
}
+ Qwerty
++ Asdfgh<sup>1</sup>
+++ Poiuytr<sup>2</sup>
+++ Mnbvcx<sup>3</sup>
+++ Kjhgtr<sup>4</sup>
++ Zxcvbn<sup>1</sup>
+++ Lkjhgf
+++ Cftred<sup>3</sup>
+++ Sderfg<sup>5</sup>
title Title
legend top
<sup>1</sup> Kietwgd.
<sup>2</sup> Kagetft.
<sup>3</sup> Nastedy.
<sup>4</sup> Paetrg.
<sup>5</sup> Hwywtw.
endlegend
@endwbs