I´ve try a couple of times in 3 websites that i use stellar to update
System - Helix Ultimate Framework from 1.1.1 to 1.1.2
shaper_stellar Template from 1.2 to 1.3
when do that, website missconfig all custom css
only error that i found is related with plugin Helix Ultimate based template installer
when clcick says
An error has occurred.
500 The file TmplHelixUltimate.xml could not be found.
to resolve the missconfig I restore the websites
the references that i found in the forum not resolve my issues
actually config is stellar template 1.2, joomla 3.9.18 php 7.3
best,